http://www.effingpot.com/slang.shtml that’s a good source for British slang terms.
I wasn’t the one with the crit about the Americanisms; but I was putting in my input. It’s fanfic and Tom’s been around a lot of Americans. I think some slips are very forgivable.
I’m throwing a lot of this off the top of my head. So.
A Brit would never say things like, Tylenol or acetaminophen. It’s paracetamol.
Or Airplane. It’s an aeroplane.
Or baby carriage. It’s a pram or a pushchair.
or booger. it’s bogey.
or cell phone. it’s a mobile.
costume party is fancy dress
counterclockwise is anticlockwise
diaper is nappy.
dishwashing liquid is washing up liquid
drug store is a chemist
dumpster is a skip
don’t ever say, “fanny pack” because reasons.
freeway is motorway unless he’s driving on a US freeway.
gasoline is petrol
to play hooky is to skive off
mail is post
plastic wrap is cling film
scotch tape is sellotape
sidewalk is pavement
curb is kerb
sneaker is trainer or plimsolls
British didn’t normally say that something “sucks,” but from what I understand it’s working its way in, plus don’t forget that Tom’s been around a lot of Americans in his business and it’s probably reached his vocabulary, along with some other Americanisms. I think with some things it’s very forgivable.
vacation is holiday or hols
washcloth is a flannel
also for spelling. British spellings rarely use the zed, and it’s often replaced by s. As in analyse or realise. Or the c vs. s in defense vs defence. Also watch the ou and u differences as in behaviour or behavior. And the er/re difference like theatre and theater or centre and center.