You would need to get an Apple iTunes account for the UK. You can not transfer your Spanish account to it, so if you decide to do so I recommend you switch as soon as possible; though it is possible to juggle two accounts if you don't mind keeping track of what was bought in what store.
Here are the instructions for setting up an iTunes account without a payment method. It's easy enough to do it with a payment method as well. You probably need to sign out of the App Store before doing this. You'll find the button for this at the bottom of the Featured tab in the App Store. The iTunes and iBooks stores have to be logged in and out of separately, so don't forget to go back and log them in with the new Id when you are done.