Question. I have been seeking for a long time now the details of the case where a reasonable man is defined as “the man on the Clapham Omnibus”.
Answer. First use of the phrase is attributed to Lord Justice Greer, in Hall v. Brooklands Auto Racing Club (1933) 1 KB 205, at p 224. The facts of that case were that a racing car shot into the air over the kerb and the grass margin and into the railing, killing two spectators and injuring others; the racing club was held not liable as the accident was unforeseeable.
Source. Many sites refer to the case and a few attribute it to Lord Justice Greer, but Asif Tufal’s a-level-law provided the facts (at Negligence – Breach of Duty – Cases).
Asif Tufal is Head of Law at a Sixth Form College in Essex and a Senior Examiner for a major exam board.
My comment is in the form of a question about when historically the concept of volenti non fit injuria became evident.
Sheriff. You sent me off on a fruitless Google search. I suggest you refer to a leading textbook (eg Winfield or Salmond) to find the oldest case referred to as authority for application of the maxim.