You can read a lot of writing lamenting the influx of Americanisms into UK English. “Can I get a…” (instead of “could I have,” or “may I have,”), “sure” (instead of “of course”), “movie” (instead of “film”). American media is consumed globally, and is probably exported more than any other country’s media that I can think of, so you can expect the adoption of some of these “Americanisms”.
However, culture and language works both ways. The Harry Potter books and movies have certainly played a part in introducing a number of words into American English, that while they may have been understood before, are becoming more and more commonplace. The most notable is probably “ginger”, which is “redhead” in American English. Though I have seen an internet post or two claiming there’s a difference between “redhead” and “ginger”, the two are used interchangeably in the US. Now even though it’s understood in the US, it’s still a little “funny” sounding, and you probably wouldn’t use it with a straight face as a descriptive term, and it’s not overly-positive sounding to our American ears.