It isn't likely to be a problem unless you get stuck with a real jerk of an immigration officer when you come through the airport. But chances are they will just "stamp you in" with little or no comment.
If you are going to be doing a lot of traveling, with many re-entries into the UK, then it's probably a good idea to have your visa reissued next time you can get to NYC. It takes only a few minutes if you're one of the first people in the morning.
I really do not understand why the Consulate isn't more careful when they issue these things. Mine had a rip down the right hand side of it which partially obscured the visa number. The IO at the airport was very nice about it when I came through, but still, they had to have the forgery experts look at the visa and I was standing there sweating bullets until they came back and said it was all right. Believe me, I had it changed the very next time I was in New York.