One notable example of how American English (or at least one idiom) shifted back to the mother country occured in the Mike Leigh film Secrets and Lies. I’ve read that in England, “to knock” someone means just to wake somebody up while over here it means to get a woman pregnant. Well, in S&L, there’s a scene where Brenda Blethyn’s character warns her daughter to bring some protection (i.e. contraceptives) with her on a date to make sure she doesn’t get “knocked up.”
Of course on the flip side, millions of Americans use the term “full monty” thanks to the recent Oscar-nominated film. So things do work both ways…