Part of it depends on your current employment situation in the UK. If you have a nice contract in the UK that demonstrates that you can afford the mortgage, the advice that I have gotten is that where there is a will there is a way, but the bottom line is, your US credit doesn't count.
While I do have a UK partner, we have been given advice that it will work out, though we will have to probally shop around a lot. I have a US expat friend who was by herself that landed a 350K mortgage by herself about 4-5 years ago. She was here on a work permit none the less and had a decent downpayment, but she was able to work it out.