“When William the B*stard conquered England in 1066, his next major act was not to exterminate the Brits, but rather to count them, so he could tax them — the Doomsday book.”
By the way, I realize you probably know little about history so your mistakes are understandable, but I thought I should remind you that there were no “Brits” in England in 1066. The people were Anglo-Saxons. There were the Welsh - but in Wales. There were the Breton - but in Brittany. If you’re going to talk about a country, I suggest you actually learn (if you don’t know already) who actually lived there and when.
I'm certain, since you are an expert on all things historical, that you already know: the name "British Isles" dates back to Ancient Greece, circa 500 BC, was used by the Roman conquers, and western civilization in general throughout history.
Yes, the word "Britons" referred to original inhabitants, who later got pushed aside by Anglo-Saxons and others.
But even by 1066, the original British still lived in Wales, Cornwall & Scotland.
In summary: since 300 BC the name is "British Isles", and the people there called "Britons" by outsiders, regardless of what they may have called themselves.