There was The Day the Queen Flew to Scotland for the Grouse Shooting by Arthur Wise. This told the story of a civil war between the North and South of England and may yet become relevant.
A few years ago I was a member of Leicester Writers Club alongside the former Labour MEP Mel Read.* She mentioned have read the book and I surprised myself when I was able to tell her who wrote it.
And there was After All, This is England by Robert Muller.
This told the story of how a Fascist dictator came to power here. It was closely based on the rise of Hitler and a post on The Numinous Book of Review will tell you all about the plot.
It will also tell you about the author:
Muller was an interesting writer, a German who settled in England after the war, and who doesn't really get the attention he deserves for the contribution he made to British cultural life; apart from this novel (and several others) he was very active on British television, penning several series, including Supernatural for the BBC in 1978, a rather splendid anthology of horror stories; and he made an outstanding contribution to the BBC's seminal science fiction series, Out of the Unknown, as well as ITV's Mystery and Imagination in the late 60s, writing blazing adaptations of Frankenstein and The Suicide Club, no less.
It is a matter of regret that his name seems to have disappeared so mysteriously... to complete the sentence of the title: It couldn't possibly happen here; after all, this is England.