The film's U.S. distributor thought that it was too long; therefore, two of the five segments, "Christmas Party" and "Golfing Story", were both cut. This confused U.S. audiences, who could not understand at all what Michael Allen from "Christmas Party" was doing in the nightmare montage at the end of it. The two segments have since been restored to all U.S. releases of the film.
What Sally is told in the film of Francis Kent being murdered by his sister is based on an actual event. Francis (aged nearly 4 years old) was murdered at Road Hill House in 1860. His half-sister Constance (who was 16 years old at the time of the murder) was arrested and put on trial in 1865. After serving 20 years in jail, she was released and emigrated to Australia, where she died in 1944 at the age of 100, one year before the release of this film. In 2008, author Kate Summerscale published a book titled "The Suspicions of Mr. Whicher", which introduced the theory that Constance either had not acted alone or had falsely confessed to the murder to shield another member of the family. There was also an episode of a TV series which had the same name as the book and that was based on it titled The Murder at Road Hill House (2011).
Cosmologists Fred Hoyle, Thomas Gold and Hermann Bondi developed the Steady State theory of the origin of the universe, an alternative to the Big Bang theory, after seeing this film. They said that the circular nature of the plot inspired the theory.
Hugo Fitch was supplied by 'The Military Ventriloquist' Arthur Brough, father of Peter Brough (a subsequent radio vent with dummy Archie Andrews) - not to be confused with the Are You Being Served? (1972) actor - who also provided the doll's voice. It was called Tim, and had long been part of his popular music hall act.
Googie Withers, when interviewed on an Australian TV midday show in the 1980s, revealed that only one take was possible in the mirror smashing scene in the film, as Ealing Studios' budget did not extend to more than one mirror. So, she gave it her best shot.