More HP Britishisms
A couple more British words that survived the Americanization of Harry Potter and the Order of the Phoenix: judder (which I see fairly often in submissions by British authors, and almost never in stories by American authors), chunter (not to be confused with chunder, Australian slang for vomit, best known in the US from the song "Land Down Under," your earworm for today), and chuffed (you'll have to click the word in the list of matches).
There's a Dictionary of British Words in the Harry Potter Books that's not bad, though its entry for chuffed leaves out the main relevant definition.