Q: changing my Apple ID from a USA account to a UK account - how do I do this?

CHANGING APPLE ID/EDIT ACCOUNT INFORMATION/CHANGE ITUNES COUNTRY

Tap Settings / iTunes & App Stores, then tap the Apple ID signed in. Sign out of the current Apple ID account and then sign in with another account or create a new Apple ID http://support.apple.com/kb/HT2731?viewlocale=en_US

Go to settings/facetime and tap the ID there and log out and log in with new ID.

Go to settings/messages and turn off imessages wait 30 seconds and turn it back on, go to “receive messages  at” tap on the ID there, sign out and sign in with new ID.

Go to settings/icloud and delete the account and when prompted select “keep information on your device” then turn it back on with the new ID.

To edit account information tap Settings / iTunes & App Stores / Apple ID: / View Apple ID

To change your iTunes Store country, sign in to the account for the iTunes Store region you would like to use, tap Settings/iTunes & App Store/Apple ID/View Apple ID/Country/Region

Read this article for information http://support.apple.com/kb/HT1311

But you still need to be in the country where you have the valid billing details to be able to download apps.  You cannot simply change the country and expect to be able to download apps from that  country if you are not physically there.  Your IP address gives you away

If you change the country and try to download and you are not in that country and/or do not have valid billing details for that country you are likely to encounter error 1009