The robbery at the beginning of the film took place in Cheney Street near its junction with Battle Bridge Road, immediately to the west of Kings Cross station.
The tunnel mouth is the south end of Copenhagen Tunnel, the second tunnel on the main line out of King's Cross station. There are real houses in the area, but the rear exterior of Mrs. Wilberforce's house is a set built in front of a blank wall. Exterior scenes at the front of the house were shot on Argyle Street, about 3/4 mile south (see goofs entry); the interiors are a studio set.
The producers originally rejected director Alexander Mackendrick's choice of Katie Johnson for the role of Mrs. Wilberforce on the grounds that she might be too frail for the project, and so they cast a younger actress - who died before filming began.
The picture of Mrs. Wilberforce's late husband above the fireplace is actually a painting of Alec Guinness in his role as "The Admiral" in the earlier Ealing Studios comedy, Kind Hearts and Coronets (1949).
Mrs. Wilberforce's husband died when he "remained at the salute on the bridge" when his boat was going down. This is how The Admiral, played by Alec Guinness, died in Kind Hearts and Coronets (1949).
William Rose claimed to have dreamed the entire story from start to finish.
When the parrot flies out of the living room and into the hallway it clearly says "Alec Guinness" as it lands.
The Packard motor car used by the thieves as a getaway vehicle belonged to Michael Balcon.
Premiere voted this movie as one of "The 50 Greatest Comedies Of All Time" in 2006.
Tommy Cooper was suggested for the role of One-Round but stage commitments prevented him from auditioning.
The piece of music that the gang pretends to rehearse is the Minuet from Luigi Boccherini's "Quintet in E major, Opus 11, Number 5". Each time one of the gang members is killed, the arrangement of the music changes from quintet to quartet to trio etc, as if it is being played only by the surviving members of the gang.