You're going to find it pretty impossible to ride exclusively Western in the UK. I suggest you dump your prejudices about English riding in the bin, and get yourself down to the local riding school. You'll have to wear a riding hat - no school can operate without one, you'll have to wear boots with a heel, and after a couple of lessons in jeans you'll probably choose to buy yourself some Jodphurs
Certainly there are Western riders and coaches in the UK, but not many. You will find it easier starting English and switching to Western.