The phrase was first put to legal use in a reported judgment by Sir Richard Henn Collins MR in the 1903 English Court of Appeal libel case, McQuire v. Western Morning News. He attributed it to Lord Bowen, said to have coined it as junior counsel defending the Tichborne Claimant case in 1871. Brewer 's also lists this as a possible first use.
who said the man on the clapham omnibus
Sir Richard Henn Collins MR