The Haunted House of Horror, which I have never even heard of, much less watched when it was originally released. It's an unusual film, more a crime thriller than a horror movie, though it does have its horrific moments (it's reminiscent in this of the Christopher Lee movie from that period, Theatre of Death), and was a lot more fun than I originally expected.
Set during the swinging sixties, it at least managed to get the look and feel of the times better than its contemporary, Hammer, usually did. Of course it helped that it was filmed then, but it's surprising how film makers so often failed even then to get it right. Some lovely colour photography too. And the street scenes are brilliant, especially of Carnoby Street. The "haunted house of horror" itself definitely looked the part.
Curious fact: The film was selected by Quentin Tarantino for the First Quentin Tarantino Film Fest in Austin, Texas, 1996.
Surprisingly, I have just read that "the film was drastically re-written, re-shot and re-cut by
writer/director 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."