I don't know what your exposure to American comedians in England is, but if it's like America's exposure to British comedians than you're probably only getting the most mainstream comedians. Somehow Carlos Mencia, Sarah Silverman, and Larry the Cable Guy are all mainstream and they all suck. They spend more time thinking of stuff that's not funny but seems ballsy to say and they know people will agree with. They spend more time getting an applause from a retarded crowd then getting laughs from said crowd.
Jimmy Carr is the only British comedians who's names come to mind, but I've seen plenty of British comedians that were pretty funny. For American comedians I like that haven't been said, I like Daniel Tosh. Oh yeah, inb4Ceej.