You need to really think about how important UK as opposed to US customers are. If you host in the US and you have a .com, you won't appear in Google UK only searches. This is only important if your location could be important to you customers though - i.e. if you ship something. Spelling and word choice can be a factor too - you won't get many UK customers visiting a site optimised for "blue colored widgets".
Also Google's definition of a UK host is imperfect - some UK IP addresses still do not show up in Google UK searches, so you should check other sites from the same host before you sgn up.
As sullen said think about UK/US spelling. A month ago I spent a couple of days trawling through the internet trying to find out how to change the colour of a photo in Fireworks. Obviously no search engine gave me anything of use, and neither did the macromedia website which I couldnt understand. Finally days later I posted on a macromedia forum and then twigged. It's a shame google didnt prompt as it does for misspellings.
If you really want to target UK customers then why not have a subdomain with country specific information. ie international telephone number, different p&p rates, returns policy...