The film was shot at Oakley Court, a Victorian Gothic country house in Berkshire, England, which previously was the home of Hammer Films. Three years later, El show de terror de Rocky (1975) would also be filmed there.
Without permission, producer Max Rosenberg attempted to use the title "I Have No Mouth and I Must Scream" taken from the popular short story by Harlan Ellison. Ellison blocked this attempt in the Federal District Court of Los Angeles.
Although he is second-billed as one of the stars of the film, Herbert Lom does not appear at all until the last quarter of the film, and only in an extended flashback sequence.
As the project was entitled "Fengriffen" all through the production process, both stars Ian Ogilvy and Stephanie Beacham later claimed having been astonished at the time by the title under which this film finally came out. Producer Max Rosenberg had set his mind on an apparently more commercially sounding title.
This was one of the few Amicus horror productions to be set in the past. Most of its horror outings, unlike Hammer, were set in recent times.