This question puzzles me. I can't properly "do" an English accent however hard I try, and
I've been in London for four years. Actually, I'm visiting New York for the whole summer,
and did have a reverse culture shock for a few days in which I used the word "takeaway" instead of "to go" and couldn't get over how "mind the gap" has come here in the form of "watch the gap" on the Long Island Railroad (yes, I'm from L.I.). I also asked a gent where the toilet was instead of the bathroom, and he made a face. So, yes, a little British vocabulary has crept in, but that's about it. I should say that when I first came to England I had a lot of trouble understanding people, and now I don't. So my receptive skills for Sarf London accents have improved, but it has not made a dent in how I speak.