Boris Karloff became ill with pneumonia while shooting this project in the freezing rain. It was his last British feature, begun January 22 1968. Karloff had just finished Targets and would recover enough to shoot four Mexican features in May 1968, his final screen work.
German Import DVD has two Super-8mm Versions (English language), as a special feature on the disc.
In its U.S. laser disc edition from the 1990s, the music track of the film was totally modified in favor of a more modern tone score.
The house used in the film is Grim's Dyke House (now a hotel) in Harrow Weald, Middlesex. The house was formerly the home of William S. Gilbert of Gilbert & Sullivan fame.