at 775; O'Donnell v Murdoch McKenzie & Co, 1967 SC (HL) 63, per Lord Upjohn at 71 and Lord Wilberforce at 73; and Davidson v Duncan, 1981 SC 83, per LJC Wheatley at 89. In O'Donnell, for example, Lord, be exceptional; the normal rule is that stated by Lord Upjohn in O'Donnell, and special circumstances