Unknown book: nuclear power station demon and child sacrifice


New Member
Jun 29, 2020
Hi - when I was at school (around 1985) my teacher read us a story which I loved and would like to reread.
Main character was a young boy who was kidnapped by a secret organisation and the story culminated with an attempted child sacrifice in a nuclear power station. The sacrifice was to summon a demon and the imagery of the floor turning to glass and the demon appearing below was fantastic.
I remember that when they failed to sacrifice the boy someone said, “one of the seven!” Believe it was set in England, but couldn’t be sure. That’s all I can remember I’m afraid.
I have no idea of the title, author, cover or date. Any ideas what this might be?
That's so 70s British SFF it hurts. I wouldn't be surprised if the Scarfolk parody was inspired by it.

Sadly, I have no actual answer.