Simple: THERE ISN"T ONE!!!
Saying "British Accent" is just as stupid as saying "North American Accent", in as much as "Britain" is more a reference to the land mass that contains within it the countries England, Scotland and Wales, so also North America contains The U.S.A., Canada, Mexico etc.
We here in The U.K. like to be called by our country of habitat, namely, England, Scotland, Wales, or Northern Ireland. (Please never get the Northern Irish Mixed up with Irish or any other english speaking accent.. They hate that just as much as we hate to be called British.) All of this hangs nicely around our accent. According to the country we live in, we like to be known as having English, Scottish, or Welsh accents. Keep calling us British, or saying that we have a British accent, and we'll start calling you Americans "Canadian" or even "north American". And we might even say that you sound like the Canadians, we know you'd hate that, but the thing is, we can actually tell the difference.
(PS:Northern Ireland is not officially classed as being in Britain, though the British government does rule it, just as it used to rule many other countries around the world. Thats why it is often referred to as Great Britain and Northern Ireland. Together this is referred to the United Kingdom, something that is totally different from Britain.)
Generic American "hero" in Generic crap
film: we know he's the bad guy, he has a British accent..
All who watch the film (outside the U.S.) think: Stupid American tosser, its just a thick Yank trying very hard to do a cockney accent, and failing miserably. Plonkers.
Not a language - A throat infection.
Guy from England: Dude, He sounds like he ha's got a real sore throat !!
Guy from Norway: No, he's speaking Danish.
Guy from England: Sounds like a throat infection to me...!