I caught myself saying "quid" instead of "pounds" after being here for a week once!! Hahahahaha. I probably go between quid and pounds equally.
Half the time I say elevator, the other half lift. I don't say "to mah to" though because I think it makes me sound pretentious.
I think it's hard to tell sometimes, I'm unaware of using British slang and British English and I actually am.
"Reckon" is one of those funny words that you hear in British English (and perhaps Australian, I don't know) as well as Southern English but I never said it even when I was in The South! But I use it sometimes now.
My mother thinks I have an English accent but I don't and neither does my best friend. I think I sound as American as the day I left!! And I still use lots of exclamation points too!!! I think I've gotten into more of a Southern as opposed to Midwestern accent though. I still pronounce pin and pen the same way.