It was only a matter of time. You can’t keep an old imperialist down.
I’m not in the least surprised about the fish-and-chips. They’ve just opened a chippie around the corner from where I live, called the Codfather. I went in to get a fish supper on the first Friday it was open, and it seems the whole neighbourhood had the same idea. I saw half a dozen people I knew in the great snake of a queue, and waited a good three quarters of an hour to be served. It was pretty tasty when I finally got it home to my starving family. Quality will rise to the top, and French food is a fad it seems, even in Paris.
The Britishisms appearing in American English is perhaps more surprising. The taste of fish and chips speaks for itself, but the arrival of slang loan words and phrases usually signals a cultural dominance, but Britain hasn’t exercised cultural dominance over the USA since the Mayflower set sail. The trend is said to have sprung up with the arrival of Harry Potter and Downton Abbey on American TV, and that may be the explanation. It is also worth remembering that the considerable spike in the data is partly explained by the fact that previous penetration of British slang or expressions was near zero.
And needless to say, the reverse current is still vastly stronger. I teach American alternatives, more in grammar or usage than in individual lexical items, as a matter of routine – it would be a stiff-necked teacher who still insisted on the present perfect with just, for example (I think I’m as likely to say ‘I just had a coffee’ as ‘I’ve just had a coffee’). And I only just found out that ‘Can I get a pint of Adnams?’ sounds wilfully non-standard to British ears (except for the bit about the Adnams of course).