Could you explain in more detail? Are you trying to set up a new iTunes Store account in the UK with new email address and a UK-issued credit card or prepaid iTunes card? If so, please describe where things are breaking down, including error message if any. If that's not what you're attempting, please provide more information about what you're trying to do and where it's failing. With more details I'm sure someone will have suggestions.
Absolutely! I'm at university in the US, and purchased a MBP from the US Apple store. I have a credit card issued by a US bank, but the billing address is back in the UK. I can't enter my mailing address at university, because that doesn't match the card information, and whenever I select a different country for the billing address (other than the United States) it tries to redirect me to the UK iTunes store (in which I can't update apps like iPhoto with my UK Apple ID, receiving the error message "There was an error in the App Store. Please try again later. (13)"). Thanks!
I have a credit card issued by a US bank, but the billing address is back in the UK.
Sorry, but that card won't work. The credit card has to be both issued by a bank in the country whose iTunes Store you wish to use and that has a billing address in that same country. A split card like yours, issued by a bank in one country but with a billing address in another, can't be used in the iTunes Store in either country.
You'll need a credit card that is both issued by a US bank and has a US billing address, or will need to purchase US iTunes prepaid cards.