Shot at Oakley Court, previously the home of Hammer Films. Three years later The Rocky Horror Picture Show would also be filmed here.
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.
Without any kind of 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. Elison blocked this attempt in the Federal District Court of Los Angeles.
This was one of the few Amicus horror productions to be set in the past. Most of their horror outings, unlike Hammer, was set in recent times.
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.