The words that ultimately gave us “Britain” have been in use for about 2,000 years, give or take a century or two. Politically and culturally a tremendous lot has happened in the meantime. Which is probably why we’re left with this almost indecipherable mine field.
Tell me about it. Immigrants? From Britain? Taking over (culturally) a foreign land. You couldn’t make it up. I once witnessed some drunk Bretons speaking to some drunk Welsh in their respective languages… and “kind of” understanding each other.