An accent that has never existed, American media has lead to most of the American general public confusing Britain to be the same thing as England rather than containing England, as such, the media has influenced the shared opinion that everyone talks in some sort of posh 1800s London accent, such media has also influenced the idea that tea and crumpets is popular among the "British" when in actual fact, very few people like either these days.
Most of the time people forget that Britain contains England, Scotland, Wales and Northern Ireland, all of which have their own regional accents as well.
American: Are you British?
English person: I am English if that is what you mean
American: I love your British accent!
English person: Are you retarded?