When I first looked up this film on the IMDb over ten years ago all three reviewers said the same thing: it had scared the hell out of them as youngsters, but none had seen it recently.
I finally caught up with it today and it's certainly not as scary seen today as those who saw it at the time remembered it (for me the most frightening film I've ever seen remains Larry Peerce's 1967 'The Incident'); although Mario Zampi certainly fulfilled the promise he showed here with his slick direction, with elegant and mobile camera work by Cedric Williams.
It's fun to see a young Patrick Nacnee and Dandy Nichols in supporting roles, but opera singer Lester Ferguson, although he makes an interesting and offbeat lead - and gets to sing a little - (SLIGHT SPOILER COMING:) is far too little changed (even down to the clothes he's wearing) in the epilogue supposedly set seven years later.