I say, old chap
I watched a TV movie over the weekend which featured a bunch of evil guys chasing some good guys. (And possibly a talking car.) Anyway, you could tell that one of the evil guys was extra evil, because he had an English accent, and it made me think about the markedness of English accents in American television and film. In my observation, English accents can signify (or amplify the signals) that a character is any of the following:
There are also a number of reality TV show hosts who would not have their jobs, I'm convinced, if it were not for their English accents. (Since I assume they are not meant to be evil and reality TV show chatter is hardly brainy, I suppose we're going for "sexy," here.)
On the flip side, it's interesting to think about what the lack of an English accent signifies, namely, on TV shows where a character is played by a British actor, but has an American accent. I guess it wouldn't make sense for Battlestar Galactica's Apollo to have a British accent when his dad and brother don't, nor do Chuck's aunts on Pushing Daisies, but there's no reason that Dr. Gregory House couldn't be British. Except that, for American audiences, British accents are marked, so it would distract from the character, I think. With Hugh Laurie doing an American accent, we're free to concentrate on other aspects of his character (and he was free to mock Chase for his accent).
Of course, Americans are equally stereotyped on British TV, where an American accent generally signals someone who is rich, ignorant, or vulgar. I guess turnabout is fair play.