I've looked this up myself, being as I have two exes here in the U.S. that totally destroyed my credit. From what I've read on two different financial advisers websites, your U.S. credit won't matter much going to the U.K., nor vice versa anyway, as the credit systems are structured much differently, and as of the moment there is no easy way to link between them, good or bad. I'm only paraphrasing what I read there.
Cheers