A friend of mine told me that he remembers reading a science fiction novel when he was kid in the late 1970s or early 1980s, which he has never been able to locate again. It was in English, and he got it from a library in the United States, but based on the content, he thinks the author was probably from the British Isles.
The book was old when he read it. It was probably originally written in the 1930s or 1940s, as it took place in a fictional version of the post-Second World War world. The action takes place on the Isle of Man, where the remnants of the democratic British and fascist continental factions are still engaged in a slow war of attrition. The rest of Europe (and maybe Asia) has been ruined and probably rendered uninhabitable, and the survivors on the Isle of Man have lost much of their advanced twentieth-century technology. In contrast, the Americas are relatively untouched, but the isolationist United State maintains a picket of warships to prevent anyone from crossing the Atlantic.
EDIT: My friend says that he only remembers four isolated things about the book:
1) It is the mid-to-late 20th century in the book, i.e. 'a little past nowish' from for when it was presumably written.
2) The Isle of Man is inhabited by two camps of savages, clearly meant to be the English and the Germans. They live on opposite sides and, outside of mere survival, their only other actions are to periodically raid each other. Fighting the enemy is their entire culture.
3) Europe is essentially depopulated. Africa has developed a stable, prosperous society and, say, 1930s level technology (orient express type trains, etc) and is slowly colonizing Europe.
4) America stayed out of the war that caused the destruction of Europe and has advanced technology, their picket line of ships in the Atlantic is a line of levitating heavier-than-air ships.