The UK specific Roku models all have an EU behind the model number. Just check the label on the bottom of the unit - the model should be something like 3100EU. Are you able to load the Hulu Plus channel on your unit as this is a US specific channel which I think is not available on EU models? If you are only interested in the BBC channels the 9-99GBP Sky NowTV box might also be an option.
Unlink your Roku from the existing account at the Roku store and do a factory reset of the Roku from the settings menu and disconnect the power. Install UnoDNS on your router, update your IP and configure UnoDNS for UK access and then create a new UK Roku account from the Roku store. Turn on the Roku and attach it to your new account and see if that helps.
EDIT: Anybody else notice the new Halloween background theme?
EDIT1: You can sign up for a 1 week free trial of UnoDNS (no CC necessary) which should be adequate to get your account configured properly -
www.unotelly.com