(at around 31 mins) The prominent painting in the apartment of Eve (Margaret Leighton) of Rave (Laurence Harvey) as a polo player was clearly altered from a copy of one of an American "old money" socialite and sportsman, Winston Guest, a top polo player in his day.
Several of the main cast lived up to the "dying young" part of the title. Laurence Harvey and Margaret Leighton were married in 1957 and divorced in 1961. She was made a CBE, won two Tony Awards, and died in 1976 at age 53. Harvey died in 1973 at age 45. Those of the remaining cast who also met a relatively early demise were Stanley Baker in 1976 at age 48, Susan Shaw in 1978 at age 49, Gloria Grahame in 1981 at 57, and James Kenney in 1987 at 56. As of late summer 2021, only Dame Joan Collins is still alive at age 88. Robert Morley was one cast member to buck the trend, passing in 1992 at age 84.
The gang's car, first seen at the beginning of the film, is a 1951 Jaguar Mark VII.
Hairy-chested Stanley Baker was forced to submit to a full body waxing before appearing in the boxing sequences.
A sign with the numbers "999" was above the public phones in the film. That is the universal emergency number in the UK, the equivalent of 911 in the US.