The film was drastically re-written, re-shot and re-cut by Gerry Levy (under the name Peter Marcus) at the insistence of one of the US producers. Original writer/director Michael Armstrong's commentary on at least one version of the DVD goes into this in detail: "Relatively little of the material outside the house was originally in the film and much of what remains was used differently. None of the material featuring George Sewell was shot by Armstrong and only one scene with Dennis Price [in the nightclub] was his. The motivation of the killer was changed and the relationships between the young people were considerably softened."
Carol Dilworth would later marry The Tremeloes singer/bassist Len Hawkes, they who would go on to have a child, Chesney Hawkes, together.
Boris Karloff was offered the role of the Police Inspector but health problems forced him to decline. He was instead offered a smaller role as the film's narrator but this was scrapped when his health deteriorated further.