The last two responses hit the nail on the head! It really matters alot from which sites you get your backlinks from. Try to get backlinks from either co.uk sites and/or sites that are hosted in the UK and you'll see a big increase in rankings.
I have the same problem with msn but the opsite countrys as you, im number1 in uk but on page 2 in usa results , i keep adding links to usa sites that i can but still no luck after 6 months nuthing has changes. I was told my webhost ulmb.com is in usa i hope it is mabye ill check again.. i wish i could trade countrys with you cause you want uk and i got it and i want usa and you have that lol