The cast-list at the end of the film lists the octogenarian actress Hilda Barry as "Miss Dacey", a character who is referred to in the dialogue, but never actually appears in the film itself.
During production on British Rail's Waterloo & City tube line, a train ran into the buffer stops at the end of the line at Bank station. David Hemmings, Gayle Hunnicutt, and ten extras suffered minor injuries.
The author of the original novel, John Bingham, was not only a well-known writer, but Lord Clanmorris.
Opening credits: All characters and events in this film are fictitious. Any similarity to actual events or persons living or dead is purely coincidental.