ajax, google the British Gliding Association website, to find which club is nearest to your home, then don't book a flight, just go and watch for a while. Talk to the locals. See if the ambience suits you.
People who show up early in the morning and help get out the kit are especially welcome. These are clubs, not private business, and because everyone helps out, makes the cost of flying quite reasonable.
And regarding progress, if you follow the news, the chap who safely landed his Airbus in the Hudson River after two Canada geese got cooked in his engines, was flyiing a large glider - and he used to be a gliding instructor! So altogether, whatever your plans, gliding is a very good start in learning to fly. If you can drive a car safely, flying is easy by comparison!