I've only seen "Bremain" used in the press one time, Teribus. Normally it's "Remain". But it's Brexit all the time - I don't think I've seen a single reference to "Exit campaigners".

"United Kingdom of Great Britain and Northern Ireland" MGM. Precisely - one island, one part of an island. Neither are nations. As for what they put on cars going abroad, that's a sort of colloquial slang used by the authorities, rather like the way they still talk about "MOT tests" when we haven't had an MOT for years.