OUTER HOUSE, COURT OF SESSION
 CSOH 69
LORD DRUMMOND YOUNG
in the cause
BRITISH INTERNATIONAL HELICOPTERS LIMITED
Act: Macdonald; Lefevre Litigation, Aberdeen
Alt: McClelland; Maclay Murray & Spens
2 May 2013
 On 10 November 1988 the pursuer boarded a helicopter owned and operated by the defenders from the Sedco 703 Platform in the North Sea, where he had been working for Sedco Forex, in order to travel to Aberdeen. The helicopter suffered severe mechanical problems and ditched into the North Sea. The pursuer escaped and was rescued approximately 50 minutes later. He avers that as a result he suffered and continues to suffer from post-traumatic stress disorder ("PTSD"). In December 1990 he raised the present action against the defenders in Aberdeen Sheriff Court. The ground of action on which the pursuer relies is a breach of article 17 of the Warsaw Convention, as incorporated into Scots law by the Carriage by Air Act 1961, the Carriage by Air and Road Act 1979 and the Carriage by Air Acts (Application of Provisions) Order 1967, a statutory instrument made under the 1961 Act. Article 17 of the Warsaw Convention provides that a carrier is liable for damage sustained in the event of "the death or wounding of a passenger or any other bodily injury suffered by a passenger". The question that is likely to be critical so far as the merits of the present case are concerned is whether PTSD amounts to "bodily injury" ("lesion corporelle" in French, the authoritative language of the Convention).
 After sundry procedure, described below, the defenders have lodged a minute under Rule of Court 21A in which they claim that the pursuer has inordinately and inexcusably delayed in progressing the action, that that delay has resulted in unfairness to the defenders, and that the action should accordingly be dismissed. I propose first to consider the construction of Rule of Court 21A; thereafter to set out the history of the present action; and finally to consider whether the motion for dismissal under that Rule of Court should be granted.
Construction of Rule of Court 21A
 So far as material, Rule of Court 21A is in the following terms:
"(1) Any party to a claim may, while that claim is still pending before the court, apply by minute for the court to dismiss the claim due to inordinate and inexcusable delay by another party or another party's agent in progressing the claim, resulting in unfairness.
(5) In determining an application made under this rule, the court may dismiss the claim if it appears to the court that-
(a) there has been an inordinate and inexcusable delay on the part of any party or any party's agent in progressing the claim; and
(b) such delay results in unfairness specific to the factual circumstances, including the procedural circumstances, of that claim
(6) In determining whether or not to dismiss a claim under paragraph (5), the court shall take account of the procedural consequences, both for the parties and for the work of the court, of allowing the claim to proceed".
 For an action to be dismissed in accordance with the rule, three requirements must be satisfied. First, there must be "inordinate and inexcusable delay" in progressing the claim. Secondly, that delay must be on the part of the pursuer or the pursuer's agent. Thirdly, the delay must result in unfairness in the particular factual circumstances of the claim. Rule of Court 21A came into force on 1 December 2008. It was enacted following upon a series of cases where the Court of Session held that power existed at common law to put an end to a pending action on the ground of lack of progress; the common law power was said to arise out of the Court's inherent power to regulate its procedure. It is also apparent that the Court was influenced by a similar procedure that was available in England, and certain features of the English procedure were expressly relied on.
 Counsel for the defenders made detailed reference to two of those cases as illustrating a range of matters that were relevant to the application of rule 21A. The first of these was Tonner v Reaich and Hall, 2008 SC 1, the case where the existence of the common law power was authoritatively recognized. In that case the pursuers in 1988 raised an action against a firm of architects whom they had engaged to design and supervise the building of their house. The action was sisted later that year on the unopposed motion of the pursuers. Sporadic attempts were made to achieve settlement. In April 2005 the pursuers enrolled a motion to recall the sist, which was opposed; the defenders sought absolvitor on the basis that it would be unfairly prejudicial to allow the action to continue in view of what was described as "inordinate, unexplained and inexcusable delay" on the part of the pursuers. The Inner House, reversing the Lord Ordinary, held that the action should be dismissed. While the action is notable principally because of the recognition of the inherent power, the court gave detailed consideration to the corresponding power in English law and referred to a number of features of that power with apparent approval. The guidelines adopted in the English cases are set out at paragraph  of the opinion (relying on Trill v Sacher,  1 WLR 1379, at 1398-1400 per Neill LJ). The basic rule in England is that an action may be struck out where there has been inordinate and inexcusable delay on the part of the plaintiff or his lawyers and such delay has given rise to a substantial risk that it would not be possible to have a fair trial of the issues in the action or the delay is likely to cause serious prejudice to the defendant. The burden of proof is, obviously, on the defendant. Further guidelines are as follows:
"(3) Inordinate delay cannot be precisely defined. 'What is or is not inordinate delay must depend upon the facts of each particular case'.... It is clear, however,
(a) that for delay to be inordinate it must exceed, and probably by a substantial margin, the times prescribed by the rules of court for the taking of steps in the action; and
(b) that delay in issuing the writ cannot be classified as 'inordinate' provided the writ is issued within the relevant period of limitation.
(4) Delay which is inordinate is prima facie inexcusable.... It is for the plaintiff to make out a credible excuse. For example difficulties with regard to obtaining legal aid may provide such an excuse.
(5) Where a plaintiff delays in issuing proceedings until towards the end of the period of limitation he is then under an obligation to proceed with the case with reasonable diligence.... Accordingly, a court is likely to look strictly on any subsequent delay which is in excess of the period allowed by the rules of court for the relevant step, and to regard such subsequent delay as inordinate even though a similar lapse of time might have been treated less strictly had the action been started earlier.
(11) Prejudice to the defendant may take different forms. In many cases the lapse of time will impair the memory of witnesses. In other cases witnesses may die or move away and become untraceable.
(12) The prejudicial effects of delay may depend in large measure on the nature of the issues in the case. Thus the evidence of an eyewitness or of a witness who will testify to the words used when the oral representation was made is likely to be much more seriously impaired by the lapse of time than the evidence of someone who can rely on contemporary documents....
(13) When considering the question of prejudice and, if it is raised, the question whether there is a substantial risk that it will not be possible to have a fair trial of the issues in the action, the court will look at all the circumstances. It will look at the periods of inordinate and inexcusable delay for which the plaintiff or his advisers are responsible and will then seek to answer the questions: has this delay caused, or is it likely to cause, serious prejudice, or is there a substantial risk that because of this delay it is not possible to have a fair trial of the issues in the action?..."
The foregoing guidelines appear to me to be relevant to the consideration of the present motion. Before moving on from Tonner, I should mention two other matters that arose in the case. First, it will not generally be open to the pursuer to argue that the defender has as great a responsibility for the delay as he does because of the existence of ample procedural means there could be invoked to compel pursuers to make progress. This is because it is the pursuer who decides whether or not to avail himself of the right of access to the court, and if he chooses to do so the defender has no option in the matter; his subjection to the jurisdiction of the court is compulsory: paragraphs  and . Secondly, in considering whether delay has been inordinate and inexcusable, account should be taken of the delay as a whole: paragraph .
 The second case cited to me was Hepburn v Royal Alexandra Hospital NHS Trust, 2011 SC 20. An action for damages for allegedly negligent medical care was raised in April 1998 and sisted in the following month; the injuries were said to have been sustained in November 1994. No significant progress was made until September 2004, when the pursuer's then solicitors withdrew from acting. Meanwhile, in March 2002, one of the two medical consultants involved in the case had died. In November 2004 the sist was recalled on the motion of the defenders, and the pursuer was ordained to intimate whether she wished to proceed with the action. New solicitors were instructed later that month, after which the claim proceeded. Defences were received late in December 2004 and the action was again sisted. During the period of the sist progress was made by the pursuer's solicitors, and the sist was recalled in November 2007. Thereupon the pursuer intimated substantial adjustments. The defenders lodged a minute seeking dismissal of the action, and following debate on that minute the Lord Ordinary dismissed the action in May 2008, on the basis that the case brought against the living consultant had been entirely altered and that against the deceased consultant had also been altered. The pursuer reclaimed, and the reclaiming motion was allowed. It was held that the decision in Tonner was correct and that the Court had an inherent power to dismiss an action for want of prosecution. Nevertheless, the Lord President, in particular, appeared to criticize some of the reasoning in the earlier case (paragraph ), notably the requirement that there should be an element of unfairness specific to the particular factual context. It is not necessary to consider that criticism further, however, because rule 21A(5)(b) specifically requires that the delay "results in unfairness specific to the factual circumstances... of that claim", which appears to incorporate expressly the test adopted in Tonner.
 The Lord President further suggested that the dismissal of an action for want of prosecution is a "draconian step". Consequently he thought that the unfairness in question must "be such that a 'fair trial' is no longer possible, or at least that there is a substantial risk that it is no longer possible". That formulation was said to reflect the obligation of the court under article 6 of the European Convention on Human Rights to ensure a fair trial. The difficulty with this formulation, it seems to me, is that the jurisdiction to dismiss an action for want of prosecution must arise well before any proof is heard. Consequently it will not usually be possible to state with confidence that a fair trial is "no longer possible"; instead the court must look to the future, and in that context it is in my opinion normally appropriate that the language of risk should be used rather than the language of certainty. On that basis, the primary test of unfairness must be that there is a substantial risk that a fair trial will no longer be possible. Of course in some cases it may be possible to use the language of certainty: where, for example, a critical witness has died without leaving any form of written statement, or vital productions have been destroyed without any fault of the defender. Nevertheless, it will usually be preferable to start by looking at the risk of unfairness if the case proceeds to proof.
 In Hepburn the court went on to consider the merits of the case (paragraphs -), and concluded that there was no substantial risk that the defenders would be prejudiced if the action went to proof. The pursuer had advanced an argument that, because the action had been sisted initially on the motion of the second defenders, she was not responsible for that period of delay. That argument was rejected (paragraph ) on the ground that the responsibility for progressing the action was with the pursuer and her solicitors, and she could at any time have enrolled for recall of the sist. Instead, her solicitors had apparently taken no steps during the period of the sist to obtain a legal aid certificate. After she changed her solicitors, however, the new firm appeared to have acted with due expedition in obtaining legal aid, obtaining expert reports and progressing the claim. Ultimately, the critical question was whether the defenders had been prejudiced by the delay. It was accepted that there was clearly some disadvantage, in that one of the medical consultants involved had died even before the pursuer's claim had been reformulated. The relevance of that prejudice was lessened, however, because the onus of proving her case rested upon the pursuer, and the court in assessing her evidence would be entitled to take into account the passage of time and any prejudice that the defenders might have sustained in attempting to rebut her case.
Policy underlying Rule of Court 21A
 The decisions in Tonner and Hepburn were cited by counsel as illustrating the origins of rule 21A and the policy considerations that inform the rule. I agree that considerable assistance can be obtained from those cases and from the corresponding rule in English law, which is based on a similar policy. The fundamental objective of the rule is clearly that cases should proceed with due expedition. As was pointed out in Hepburn, that objective is supported by article 6 of the European Convention on Human Rights, but it is so obvious that support from the Convention is scarcely necessary. There are perhaps two main underlying policy reasons behind the objective. First, if litigation is delayed, there is a risk that evidence will be lost: documents or real evidence may be destroyed or mislaid; and the recollection of witnesses may be impaired, with the result that relevant matters may be forgotten or an account may be given that is materially inaccurate. These policy considerations also underlie the law of prescription and limitation; in that context the excellent discussion by McHugh J in the High Court of Australia in Brisbane Regional Health Authority v Taylor, (1996) 186 CLR 51, is helpful. Secondly, it is unfair to the defender to have litigation hanging over him for a long period. In this connection, it must be borne in mind that the existence of a pending claim can have serious adverse effects on the defender, as by increasing his insurance premiums or diminishing his credit rating. It is also possible that the decision in the delayed case may have consequences for the determination of other litigation, as suggested in Hepburn at paragraph . In relation to the defender's position, too, it must be borne in mind that
"Whether or not to avail himself of [his] right of access to the court lies exclusively within the [pursuer's] choice; if he chooses to do so, the [defender] has no option in the matter; his subjection to the jurisdiction of the court is compulsory": per Lord Diplock in Bremer Vulkan Schiffbau und Maschinenfabrik v South India Shipping Corporation Ltd,  AC 909, at 977, cited in Tonner at paragraphs  and .
Thus, without such a power as is found in rule 21A, the defender might well find himself powerless to defend himself against ill-founded claims that are simply not progressed by the pursuer.
 There is a difference between these two policy considerations: the loss of evidence creates the risk of irremediable prejudice; the fact that the defender has litigation pending against him, on the other hand, can frequently be remedied by requesting the court to order specific procedural steps other than dismissal of the action. Nevertheless, mere delay can, if it is sufficiently prolonged, be considered unfair to the defender. It is also necessary to bear in mind that, even in a case where the quality of the evidence is impaired, the defender can found on the delay when the action proceeds to proof before answer. The burden of proof remains throughout on the pursuer, and any difficulties resulting from culpable delay on the part of the pursuer's advisers should generally be resolved in favour of the defender.
History of the present action
 The accident to the pursuer occurred on 10 November 1988, 24 years ago. The present action was raised in Aberdeen Sheriff Court in December 1990 and was immediately sisted. In March 1995 the pursuer changed his solicitors, instructing his present solicitors for the first time. Legal aid was obtained in September 1995, and sanction was granted to instruct counsel. A report was obtained from a psychiatrist. The pursuer's solicitors were also acting for the pursuer in Abnett v British Airways PLC, 1997 SC (HL) 26 and thought it likely that in that case the House of Lords would deal with the question of whether PTSD amounted to "bodily injury" within the meaning of article 17 of the Warsaw Convention. When the decision was issued in December 1996, however, it did not answer that question. In January 1997 the pursuer obtained sanction from the Scottish Legal Aid Board for an opinion on the merits from counsel. Such an opinion was produced in February 1997. Thereafter sanction was obtained for the production of a medical report, which was instructed in June 1997 and received in October of the same year. In November counsel requested a consultation with the author of the report. Sanction for that was granted in November, and the consultation took place early in March 1998. Counsel then indicated that he wished a report from a further expert. Sanction was obtained for that; a further expert (Dr Herbert, mentioned below) was instructed in April 1998 and reported in July 1998. That was followed by a request from counsel for further comments from the expert and another consultation, which took place on 7 October 1998. After that, adjustments were intimated to the defenders on 15 October 1998, together with a motion to recall the sist. That was heard on 21 October 1998, when the defenders moved the court to dismiss the action on account of the delay that had occurred. The Sheriff dismissed that motion and ordered the defenders to lodge defences.
 On 13 January 1999 the action was remitted to the Court of Session. A procedure roll hearing was fixed for 29 and 30 June 2000 but was discharged at the beginning of that month. On 3 November 2000 the action was sisted of consent pending a further decision of the House of Lords, that in King v Bristow Helicopters Ltd, 2002 SC (HL) 59. That decision was issued in February 2002. Although opinions were expressed on the question of whether PTSD could be said to amount to "bodily injury" within the meaning of article 17, these differed radically, and no guidance was given on the fundamental question: compare Lord Steyn (paragraphs (22]-(29]) and Lord Hope (paragraphs -), who thought that PTSD had not been shown to amount to "bodily injury", with Lord Nicholls (paragraphs -) and Lord Hobhouse (paragraphs  and ), who thought that it might well amount to "bodily injury" if appropriate evidence were available. Following the decision in King, the pursuer obtained an opinion on the merits from junior counsel in June 2002, and in July 2002 the pursuer's Edinburgh solicitors wrote to the defenders' solicitors to state that they were instructed to proceed and offering a proof before answer. They do not appear to have received a reply from the defender's solicitors.
 On 12 June 2003 the sist was recalled on the pursuer's motion. In October 2004 a procedure roll diet was fixed for October 2005, to deal with the application of article 21 of the Warsaw Convention. In October 2005, however, the procedure roll diet was discharged and proof before answer was allowed on dates to be fixed thereafter. The defenders state that the pursuer nevertheless failed to contact them to arrange such dates, and as a result no dates were ever fixed. The pursuer, by contrast, states that at about the time when the procedure roll diet was discharged the defenders' solicitors had spoken to the pursuer's Edinburgh solicitors and had intimated that they would like to see the action disposed of and would be prepared to enter into settlement negotiations. The pursuer's solicitors stated that they were not in a position to quantify the claim as investigations up to that point had concentrated upon the matters which were to be the subject of the procedure roll discussion. In November 2005 counsel for the pursuer was instructed to prepare a note on the line of evidence. Shortly afterwards the defenders formally requested a valuation from the pursuer. Consequently the pursuer's counsel was instructed to delay preparation of the note on the line of evidence. In December the pursuer's solicitors discovered that sanction from the Scottish Legal Aid Board would be required before it would be possible to prepare a full quantification of the pursuer's claim, and at the same time the pursuer's Edinburgh solicitor went off work on long-term sick leave.
 The defenders state that thereafter they received no substantial communication about the action until February 2007, when the pursuer's solicitors wrote to the defenders' solicitors to suggest settlement. Correspondence on that topic continued until 13 September 2007, when it came to an end with a letter from the pursuer's solicitors. The defenders' solicitors have had no communication from the pursuer's solicitors since then, and the defenders assert that they are not aware of any explanation for such lack of progress. They state that their solicitors have continually sought progress from the pursuer, but telephone calls and letters have gone unanswered. The pursuer accepts that correspondence came to an end in September 2007. Counsel for the pursuer informed me that by this stage the pursuer was seeking to prove that PTSD resulted from chemical changes in the brain and on that basis could be said to be a "bodily injury". Evidence was required to establish that. The expert previously engaged on behalf of the pursuer, Dr Herbert, of Cambridge University, had given an explanation of the evidence to suggest that PTSD was the result of chemical changes of that nature. Dr Herbert was medically qualified but he was not a clinician, and he thought that the necessary evidence would better come from a clinician; only a clinician could properly give evidence not merely about the underlying chemistry of the brain but also about the changes that might have taken place in the pursuer as a result of his experience. The necessary clinical evidence would be that of a neurologist, but neurologists in the United Kingdom do not treat people suffering from PTSD. As a result Dr Herbert had been unable to suggest any clinician in the United Kingdom who might be of assistance. It was apparent that the only satisfactory way of obtaining the appropriate evidence was to approach a doctor in the United States, but at this stage (2007) the Legal Aid Board was not willing to sanction an opinion from a doctor there.
 In order to deal with this problem, counsel had conducted research within Glasgow University library, where he had unearthed and copied a substantial number of medical articles and had identified a potential expert, Professor Yehuda, who was the Head of PTSD Treatment at the American Veterans' Treatment Programme in New York. Counsel had conducted discussions with Professor Yehuda by telephone in the early summer of 2008, and a note on the line of evidence dealing with medical aspects of the case had been prepared in July 2008. On 4 August 2008 the pursuer's solicitors had asked Professor Yehuda if she would accept instructions, and later in the same month the Legal Aid Board was asked to sanction her employment. Further correspondence ensued among the Legal Aid Board, Professor Yehuda and the pursuer's solicitors. Information from Professor Yehuda was sent to the Legal Aid Board on 16 October, but sanction for Professor Yehuda's employment was not obtained until 13 August 2009, following reminders sent in May, June and July by the pursuer's solicitors. The Legal Aid Board advised that the delay was caused by their losing their file. Further correspondence took place thereafter. Sanction for a report was granted on 24 August 2010, the Legal Aid Board having once again had problems in locating their file. Professor Yehuda was asked how she would like to proceed, and correspondence ensued among her, the solicitors and the Scottish Legal Eight Board which lasted until 2012. The Legal Aid Board had expressed concerns about sanctioning the employment of an American expert and had required further information. The current position was that the Legal Aid Board had been given the information requested, most recently on 21 June 2012, but sanction for the employment of Professor Yehuda to prepare a report and if necessary give evidence had not yet been obtained.
Application of Rule of Court 21A
 It was against the foregoing background that the defenders enrolled the present motion requesting the court to dismiss the action on the basis of the pursuer's inordinate and inexcusable delay in progressing it and the unfairness which that delay was said to have caused the defenders. I have set out the background in detail because it is clear that the application of Rule of Court 21A depends on the specific factual circumstances of the case. In considering the circumstances, however, it is necessary to bear in mind both the overall delay and the particular parts of that delay that can be said to result from the actings of the pursuer and his legal representatives; it is only the latter part of the delay that can be described as "on the part of any party or any party's agent", as required by rule 21A(5).
 Counsel for the defender referred to the overall delay and also highlighted a number of individual periods when, he said, inordinate and inexcusable delay had taken place. The first of these was the period between December 1990 and March 1995, following the initial raising of the action. No explanation, he said, had been tendered for that delay. The delay was particularly inexcusable in that the action had been raised immediately before the expiry of the two-year limitation period under the Warsaw Convention; in that connection, the fifth of the policy considerations mentioned in Tonner was relevant (paragraph  above). Counsel conceded that the delay after the pursuer's present solicitors became involved, when the decision in Abnett was awaited, was excusable. The second period of what was said to be inordinate and inexcusable delay occurred after that decision became available in September 1996 and extended over the following two years, to October 1998. That delay was criticized on the ground that it should not have taken so long to obtain a medical opinion. Thereafter the defenders attempted unsuccessfully to have the action dismissed when the sist was recalled in October 1998. The delay between then and February 2002, while the decision in King was awaited, was accepted as excusable. Likewise, the delay from February to June 2002 was excusable in that counsel's opinion was awaited on the implications of King. The third period of inexcusable delay was said to have occurred thereafter, between July 2002 and June 2003, the date when the sist was recalled. The pursuer alleged that during this period he was awaiting a response from the defender's agents regarding further procedure. The answer to that, however, was that making progress in the action was for the pursuer, not the defenders; all that the pursuer had done was to write once to the defenders' solicitors regarding further procedure. When the defenders' solicitors did not reply, it became the pursuer's responsibility to progress matters, and it would have been possible to have a proof before answer fixed. The fourth period of inexcusable delay was said to have occurred between June 2003 and October 2004, between the recall of the sist and the fixing of the procedure roll discussion. No explanation had been tendered for that delay.
 During the year from October 2004 to October 2005 parties were awaiting the procedure roll discussion that had been fixed, and that delay was not criticized. The fifth period of delay that was said to be inexcusable occurred during the period between October 2005 and the present. The pursuer contended that these delays were justified by the need for the pursuer to obtain expert evidence, sanctioned by the Legal Aid Board. Counsel for the defenders submitted that, while some delay might be justified, it was simply not acceptable that at a point 17 years after the accident (in 2005) the pursuer had been unable to value his claim. A period of a few months to obtain expert evidence and the delays caused by the need to obtain legal aid could be justified, but the overall period of more than seven years was inordinate and inexcusable. In particular, it was not clear why the original expert report obtained by the pursuer on the causation of PTSD was not good enough to go to proof. The explanation given for this by the pursuer was, as indicated above, that no suitable expert was available within the United Kingdom and it had been necessary to go to the United States to obtain the necessary evidence, with consequential difficulties in obtaining legal aid. On this, counsel for the defenders submitted that the need for evidence from an American expert had become apparent in the course of consultations with Dr Herbert in 1998, but steps to identify and approach such an expert and obtain legal aid for a report had not been instigated until 2008. The pursuer had the ability to construct his present case from 1998 onwards, and waiting until 2008 to do so was inexcusable. In 2013 he was still building his case.
 The last point that had to be addressed by the defenders was the question of unfairness. In this respect, it was submitted that unfairness arose in three respects. First, the specific question that had to be addressed was whether the pursuer's brain had been affected by his experiences in such a way as to cause PTSD. That question now had to be considered 25 years after the event. It could be said that the pursuer had waited for science to catch up with his claim. He required under the Warsaw Convention to prove that PTSD had a physical origin. He had not been able to do that when the action was first raised, and was not yet in a position to go to proof on the matter. It was unfair to the defenders that they should remain as a party to litigation while the pursuer waited to see whether he had any case.
 Secondly, the memories of those who could speak to the extent and effects of the pursuer's PTSD would have faded during the years that had elapsed since the action was first raised. A crucial issue was whether PTSD made the pursuer unable to work, and that would involve a detailed inquiry into the nature of his symptoms, whether they were in fact attributable to PTSD, and whether he could find any sort of work. It would also be necessary to examine other aspects of the pursuer's health that had a bearing on his ability to work; these included sciatica and back pain. In addition, he had suffered from bereavement and his wife's ill-health, which might also have affected his ability to work. The quality of the evidence available on these issues would inevitably be diminished as a result of the passing of time. In this connection, the symptoms of PTSD suffered by the pursuer were unlikely to be in his medical records, but would require to be spoken to not merely by him but by his family, friends and colleagues. Their memories would undoubtedly have suffered. At this stage it was not clear who the witnesses were who might be able to speak about the pursuer's behaviour, not whether they could be found. Nor was it clear that those witnesses could describe the pursuer's symptoms with any precision, for example by pinpointing when particular symptoms occurred. There was a substantial risk that the evidence for the pursuer would simply amount to his own assertions.
 Thirdly, on the basis of expert evidence a view would have to be taken as to whether the pursuer's symptoms were consistent with physical brain damage. After such a long time, there must be significant doubt as to whether the primary evidence would be of sufficient quality and clarity to permit experts to express a view on this issue. The court would require to weigh up such evidence in a legal context that was highly controversial. When this difficulty was taken together with the two previous factors, there was at least a substantial risk that a fair trial would no longer be possible. The particular danger was that actual recollection of events would be replaced by an accepted social narrative, representing received wisdom rather than actual experience.
 For the pursuer, counsel explained the history of the case in some detail; I have taken this into account in the narrative at paragraphs - above. In relation to the first of the periods of delay founded on by the defenders, between 1990 and 1995, it was submitted that, while the action had been sisted on the pursuer's motion, discussions had taken place, and no attempt had been made to lodge defences. As to the second period of delay, between 1996 and 1998, that period had been utilized in obtaining an opinion from counsel and thereafter obtaining the views of two successive medical experts; this had involved consultations and reports. The third and fourth periods, from July 2002 to October 2004, should be looked at as part of a longer period that began with the closing of the record in April 1999. The pursuer's solicitors had offered a proof before answer following the decision in King, but the defenders had decided that a procedure roll discussion would be appropriate to consider the application of article 21 of the Warsaw Convention (which provides a defence of contributory negligence). Eventually, however, in October 2005, the defenders had decided not to proceed with that argument, and the procedure roll diet was discharged. On that basis, the delay from 2002 to 2004 could not be considered inordinate and inexcusable. Finally, in relation to the fifth period of delay, from October 2005 onwards, attempts to settle the action had been made in the early part of that period. In addition, there had been serious practical difficulties in following up Dr Herbert's advice to find a suitable expert witness in the United States. Repeated difficulties were encountered with obtaining legal aid; these could not be blamed on the pursuer or his solicitors. In all the circumstances, it was submitted that the defenders had not established inordinate and inexcusable delay by the pursuer or his solicitors.
 Counsel for the pursuer also submitted that the defenders had not established that any prejudice would result from the delays that had occurred. The critical issue was whether PTSD amounted to bodily injury in terms of article 17 of the Warsaw Convention. This would be a matter of expert evidence, and the strengths and weaknesses of that evidence would not be affected by the time that had passed. In particular, Professor Yehuda had stated that it was not too late even now to perform the tests necessary to discover whether the pursuer had PTSD (the tests envisaged were clinical tests, physical in nature, rather than tests that required psychiatric or psychological testing). The primary evidence about the pursuer's history in the 1990s would have lessened with the passage of time, but he had been subject to a psychiatric examination already, in the 1990s. In these circumstances, it was submitted, the defenders were unlikely to be prejudiced. The pursuer might be prejudiced through the lack of primary evidence of high quality; in this connection, it was important to bear in mind that the onus of proof rests on him, and that if the defenders could show at the proof that they were prejudiced by the passage of time that is a factor that the court would require to take into account.
 I have come to the conclusion that the requirements of rule 21A are satisfied, and that the defenders' motion should accordingly be granted. Twenty four years have elapsed since the date of the pursuer's accident, and the final version of the pursuer's case has not yet been formulated; the Legal Aid Board has still to give sanction for a definitive opinion from Professor Yehuda. The lapse of such a long period is significant in itself; in my view it can be described as inordinate. Nevertheless, more detailed analysis is required before it can be held that there has been inordinate and inexcusable delay on the part of the pursuer and his solicitors. For this purpose it is necessary to break the delay down into its component parts. On the analysis advanced by counsel for the defenders (paragraphs - above), five periods were identified as culpable. The first was a period of four years immediately following the raising of the action in Aberdeen Sheriff Court, when nothing was done. I agree that this period was culpable; no proper explanation was given for this period of delay, and it followed the raising of an action very close to the two-year time limit that applies under the Warsaw Convention. The fact that the action was sisted and that no attempt was made to recall the sist is irrelevant; it is for the pursuer, not the defenders, to ensure that the action makes progress.
 The second period of delay founded on by the defenders was the period of two years in 1996-98, following the decision in Abnett, when the pursuer was obtaining medical opinions. During this period the pursuer obtained an opinion from counsel and opinions from two separate medical experts. While it cannot be said that the action was being progressed expeditiously, I have come to the view that it cannot be said that the delay during this period, taken by itself, was inordinate and inexcusable; progress was being made, albeit slowly. The fundamental problem for the pursuer, however, is that it was the consultations with Dr Herbert during this period that revealed the need to find another expert (a neurologist) if the pursuer's case was to be properly formulated. That has important consequences for the later delay. The third and fourth periods run together, extending from June 2002 to October 2004, and followed the decision in King. The only explanation given for this period of delay was that the pursuer's solicitors had written to the defenders' solicitors offering a proof before answer and had not received a reply. The answer to this is, of course, that it is for the pursuer, not the defenders, to ensure that progress is made in the action. For this reason it seems to me that this period of delay, looked at in isolation, can be regarded as inordinate and inexcusable, and also attributable to inaction on the part of the pursuer's solicitors.
 The fifth and final period of delay founded on by the pursuer extends from October 2005 to the present, seven years in total. Counsel for the pursuer explained what happened during this period, as set out at paragraphs  and  above. By this time the pursuer was attempting to establish that PTSD was the result of chemical changes in the brain and argue that it was therefore "bodily injury" in terms of the Warsaw Convention. Considerable work was required to identify a suitable expert who had both theoretical knowledge and clinical experience. Such an expert was only available in the United States, and considerable work was required to identify such a person and time was taken in obtaining sanction for legal aid; indeed, at present it does not appear that the Scottish Legal Aid Board has yet sanctioned the employment of Professor Yehuda to prepare a definitive report. The total period from October 2005 appears to divide into two parts. First, during the period from October 2005 until early 2007 there was inaction on the part of the pursuer's solicitors. In my opinion that period of delay is clearly culpable. It was suggested that for part of the time the pursuer's Edinburgh solicitor was off work, which may provide a partial explanation; nevertheless, when the solicitor responsible for a case is unavoidably absent it is important that alternative arrangements should be made, and the need for doing so is particularly significant in a case that has lasted as long as the present action. In 2007 there was a certain amount of correspondence about settlement.
 It was stated for the pursuer that at this time his advisers came to recognize that, if he were to succeed, it would be necessary to establish that PTSD was physical in origin. This, with respect, seems strange; Dr Herbert had been consulted in 1998, and he had recommended that evidence should be obtained from an appropriate clinician. He was well aware of the limits on his own expertise, which was essentially academic and theoretical rather than clinical. Furthermore, it is clear from the report of King v Bristow Helicopters Ltd, supra, that the possibility that PTSD had physical causes had been raised before that case was decided in February 2002; in the American case of Weaver v Delta Airlines, (1999) 56 F Supp 1190, it had been held that PTSD had physical causes: see King at paragraph . Thus the issue that is now said to be critical in the present case has been known about and discussed in detail for at least 12 years. It is true that Dr Herbert was unable to recommend a suitable expert in the United Kingdom, but that meant that the need to identify an expert in the United States or elsewhere was immediately apparent. At the very least, therefore, the need to obtain the evidence of an expert such as Professor Yehuda should have been noticed as early as 1998, and certainly by 2002. If that had been done, the delays that have occurred between 2008 and the present would have been absorbed at an earlier stage. No doubt other things were happening, including the defenders' intention to take the case to a procedure roll discussion on the application of article 21 of the Warsaw Convention. I do not think, however, that this absolves the pursuer's advisers from obtaining evidence about the physical origins of PTSD; that fact was critical to establishing his case, and thus should have preceded everything else.
 During the period from the summer of 2008 until the present, a number of actions have taken place. In 2008 counsel prepared a note on the line of evidence, Professor Yehuda was contacted and the Legal Aid Board was asked to sanction her employment. Thereafter there were very major delays in obtaining sanction for detailed areas of work by Professor Yehuda. These delays were in large part of the fault of the Legal Aid Board, which appears to have mislaid the file on two separate occasions for significant periods. Much of the difficulty appears to have arisen out of the fact that the Board was reluctant to pay for the services of an expert in the United States. Limited sanction was obtained, but there has still been no comprehensive sanction for the preparation of a detailed report on the merits by Professor Yehuda. Clearly much of the delay during this period has been caused by the Legal Aid Board, and to that extent the delay cannot be said to result from the actings of the pursuer and his solicitors. The Board's attitude is no doubt driven by their limited budget, and by the fact that obtaining Professor Yehuda's opinion following an examination of the pursuer would be an expensive exercise. It has, however, lost its file on two occasions. The fundamental problem, however, is that the need to consult an expert such as Professor Yehuda in order to put the pursuer's claim into a suitable form was apparent when Dr Herbert was consulted in 1998. Thus, while the delay since 2008 are not attributable to inaction by the pursuer's solicitors during that period, they are attributable to inaction at an earlier stage. It is that inaction that in my opinion makes this period of delay inordinate and inexcusable, and attributable to the actings of the pursuer's solicitors. Moreover, in view of the very long time that the action had taken, there was good reason for ensuring in 2008 that matters were progressed expeditiously. As I have mentioned, establishing a physical origin for PTSD was critical to establishing the pursuer's case
 On the foregoing basis, the total periods of culpable delay amount to 13 years or thereby out of the 24 years that have elapsed since the date of the accident. That is a substantial period. It must, moreover, be considered in the context of the great length of the delay that has occurred since the accident. While the overall delay has resulted in part from legal difficulties that have arisen under the Warsaw Convention, which have been considered at length in Abnett, King and numerous cases in other jurisdictions, I am of opinion that the pursuer's case should have been approaching a definitive form long before now. Consequently, taking the total length of the delay and the couple elements together, I consider that the delay is inordinate and inexcusable and results from the actings of the pursuer or his agents.
 The second question that must be considered is whether such delay has resulted in "unfairness specific to the factual circumstances, including the procedural circumstances, of [the] claim". In my opinion this part of the test in rule 21A has been satisfied. I reach this conclusion for two principal reasons. First, the symptoms of PTSD, if established, must have existed over a period of 24 years. The pursuer's case is that he suffered PTSD from an early stage, and it contains averments about the difficulty that he had in finding and keeping jobs in the 1990s. Thus the early manifestations of PTSD, if they are established, must be of considerable importance. The written records are not likely to be extensive; the pursuer may well have consulted his general practitioner, and it is said that he had been the subject of psychiatric examination during the 1990s, but much of the impact must be on his ordinary life, whether at work, socially, or at home with his family. That impact is unlikely to be documented. Moreover, it is not clear what supporting witnesses are available. In view of the time that has elapsed, there must inevitably be severe doubts about the quality of evidence about what happened during the 1990s, especially in the absence of documentation. This problem relates not merely to the pursuer's difficulty in finding and keeping employment; it relates to the overall effect that PTSD had on his life. It is therefore central to the pursuer's case. There is in my view a very substantial risk that the defenders will not be able to test the evidence about the pursuer's state during the 1990s because of the poor quality of evidence that is available.
 Secondly, there is in my opinion a significant risk that the defenders' ability to test the expert evidence relating to PTSD will be impaired by the lack of good evidence as to what happened in the first 15 years or thereby after the accident. The pursuer claims that a diagnosis of PTSD can be made on the basis of clinical tests alone, but that may well leave open the question of how seriously the particular pursuer is affected. Moreover, the pursuer has only raised the issue of physical causation of PTSD at a fairly late stage in the history of the action. This means that the defenders have not been able to have examinations or tests carried out at a stage relatively soon after the accident, which could well result in prejudice. It accordingly appears to me that there is a significant risk that the delay that has occurred will result in important prejudice to the defenders in countering the pursuer's evidence on the causation and the effects of the particular symptoms that the pursuer suffered. It is true that at the proof the burden of making out his case rests firmly on the pursuer, and that the defenders would be entitled to draw attention to any prejudice that had been caused by the delay. Nevertheless, the fundamental problem resulting from the lapse of time is that the evidence presented is likely to be incomplete and vague in important respects. That is a hopelessly unsatisfactory basis on which to conduct a proof where both medical and legal issues are likely to be difficult.
 For the foregoing reasons, I conclude that the requirements for dismissal of the action under rule 21A have been met. I will accordingly grant the defenders' motion for dismissal of the action. I should add, however, that I have not found the issue especially easy; rule 21A is a relatively recent innovation, and there is no direct authority on its construction. In conclusion, I should thank counsel for their very detailed and helpful submissions.