try <a href="http://www.gliding.co.uk" target="_blank">www.gliding.co.uk</a> for a complete list of gliding clubs in the UK (it's the BGA's website)
To add to further replies; Lasham is very good (about the best in terms of club fleet/ facilities) in the UK. But its size means it can be very impersonal, even to other glider pilots. It's also thermal only (in the main), so if you were thinking of flying now it's alot of circuits of high aerotows. Lasham is also very expensive... but you get what you pay for.
If you were thinking of learning over the winter, then try Dunstable (London GC). They ridge soar on the downs, and as long as the wind is blowing against the hill (w, nw I think) you can fly. So all winter, as well as all night etc. I think they used to to duration records there... 20+ hours were flown, in the 1930's. It was stopped after pilots fell asleep and died etc... anyway, I digress...
Also near London are Booker (High Wycombe), but you have to share this with power, helicopters and no apparent use of ATC, for the gliders anyway. Keeps you eyes looking out of the window I suppose. However, it's aerotow only, which can be more expensive, and a mainly thermal (ie summer) site. You will also have to re-solo for winch launching.
There are also smaller places; Surrey Hills at Kenley - a small site on top of the hill almost in London... but they only have a small triangle of airspace in which to go up, and not much further!
If you can blag some connection with the RAF, you can try RAF Halton, which is RAFGSA... very cheap flying (and drinking). But a closed shop for civvies.
Hope the above is of some use. Check out the BGA's web site, find a club and pop along one weekend to see if you like the place. Gliding clubs are pretty friendly places, and another pair of hands to push a glider about won't be refused...! You'll learn alot even of you don't fly, and get a good feel for the place. If you like it, stay, if not try somewhere else!