Reputable suppliers I buy from are located in U.S. (MobileSentrix, Group Vertical, etc.), I believe they ship to U.K. (ask for shipping charge estimate before you place an order).
Some nuances you should look out for between a premium and average iPad digitizer:
* Premium comes with Tesa 61395 adhesive, average comes with generic less tacky adhesive.
* Premium has bronze colored frame, average has silver colored frame.
* I have seen many false advertising where they put pictures of premium digitizer and sell you an average one, make sure what you see on the picture is the actual product you will receive.