Normally speaking I’d claim a novel written in the 1930s and set in the late 40s for science fiction. But this doesn’t quite reach the threshold. There are around three obvious things that are futuristic: a reference to the Anglo-Nicaraguan war of 1946; ‘air mail’, where a package sent from London is dropped into a field in Sussex; and the astonishing combination of phone and television, allowing the callers to see as well as hear each other! Or rather, one caller to see the other, since phone boxes don’t have ‘television dials’ (but must at least have cameras).
Oh, and the train service has become rubbish, not because of the car or Beeching, but because (wealthy) people mostly fly.
But all that is nothing compared to how funny and overall good this novel is. Stella Gibbons wrote many other novels, but all of them are out of print but this, which is a great shame.