I remember very little of AN ENGLISHMAN'S CASTLE. The title, by the by, is a nod to AN ENGLISHMAN'S HOME, a 1909 smash hit play about an invasion of England by forces meant to be German. Does it end up with the soap opera being used to give the signal for an uprising? IT HAPPENED HERE- Interesting, but amateur. Understandably so given that it was an amateur production made for virtually nothing. There's a book in the old CINEMA ONE series about how it was made that you might be able to dig up. It's by Kevin Brownlow who was one of the film makers. The best handling of this theme is THE OTHER MAN (1964). There was a novelised version by the scriptwriter, Giles Cooper. Set mainly in a British army unit in India. It's never resurfaced as far as I know. Perhaps difficulties about rights- it starred Michael Caine, made just before he became famous.