Go to the store in iTunes on your pc then sign out of iTunes.
At the bottom of the page in the right hand corner you will see a little round flag, it should be your countries flag, click on it, then choose the UK flag, which will take you to the UK Store.
Go to download the app you want and when it asks you to sign in, click on create an Apple ID. Create a new ID, but when it asks for credit card details choose none and when it asks for your address, then you need to enter a UK address.
To get a random UK address, go to Google Maps and find somewhere in the UK and use the address. Pick somewhere that is unlikely to be the address of an existing user, like a bus depot.
Once you have confirmed the new Apple ID, you can download free apps from the UK store. I have done this for the US store and the Spanish store. Works a treat.