Lynne Murphy, proprietress of the Separated by a Common Language blog, has since 2006 selected the most noteworthy words that have traveled from the U.S. to the U.K, and the other way round (AmE: “around”). Here are her past U.K. to U.S. selections:
2006: wanker
2007: (baby) bump
2008: to vet (e.g. a candidate)
2009: to go missing
2010: ginger (redhead)
2011: kettling
2012: bollocks
2013: bum
The links go to her posts. I have covered all except “kettling,” which I confess I wasn’t aware of until today; you can find my entries by putting the words into the “Search” function.
Drum roll, please. This year Lynne chose both an adjective and a noun: “dodgy” and “gap year” (links are to my posts). And her U.S. to U.K. winners? “Awesome” and “bake-off.” Awesome.
notoneoffbritishisms.com 
Awesome: so not. Possibly the very worst word-import ever. Augh! Please take it back. We already have ‘ya know’ and ‘like’ ad nauseum.
“Kettling” has an interesting history: http://nancyfriedman.typepad.com/away_with_words/2011/10/word-of-the-week-kettling.html
Interesting, because “kettling” is the one that’s new to me, too.
A Canadian, I first became aware of this word in 2010.
From the Globe and Mail “A senior police officer who ordered the arrests of hundreds of people during Toronto’s G20 summit four years ago had no regard for their conduct or intentions, a prosecution lawyer told the officer’s disciplinary hearing on Wednesday. Superintendent Dave (Mark) Fenton has pleaded not guilty to a total of five charges of unlawful arrest and discreditable conduct stemming from two “kettling” incidents that occurred over the summit weekend.”
I’ve never heard anyone in the UK say “kettling”, and until now never seen it written, either.
Talking of “UK” – we never (or very rarely) punctuate it so that it becomes “U.K.”