Try the BGA website
http://www.gliding.co.uk/findaclub/ukmap.htm
There are intensive courses, but like everywhere in the UK, the weather isn't always helpful. Given decent weather and suitable ability it is just about possible to solo by the end of the second week - but don't count on it.
I'd recommend London Gliding Club at Dunstable, Lasham, Booker, Yorkshire Gliding Club, Husband's Bosworth, Bristol & Glos, Black Mountains and the Bidford Gliding Centre
My old instructor used to say, if getting solo is important to you, go to a flat site, like Lasham. If you want good skills, on the other hand, go to a hill site...
Whatever you do - do try it.