- 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).
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