I got an extension on my taxes, so haven't actually done it yet, but my impression was that you would still be able to direct deposit into a US bank account, but I am not sure about a UK account. I don't think you would be able to.
You can contact the IRS at the US Embassy in London by calling: 020 7894 0477 (which never worked for me) or e-mailing them at: irs.london@irs.gov (they got back to me within about a week when I was asking about extensions)
If you find the answer to your question, I would love to know as well, so can you please post it on here?