I see you're flying in yorkshire. If you're interested in gliding, try the Yorkshire Gliding Club at Sutton Bank. It's a fantastic place to fly and there are several schemes for younger members and students.
I can't remember the exact figures, but membership would be extremely cheap for you. Compared with powered flying, it works out a lot cheaper, especially if you winch launch. They also have a wooden single seater with free hire for students so all you have to pay for is the launch.
As has been pointed out, you still cant go solo untill you're 16, but there are a lot of things you can do in the mean time and there is the advantage of a club atmosphere.
They are desperate to attract new members and the two seaters are under utilised, so it might be worth giving them a ring.
Their number is 01845 597237 or the email address is
www.ygc.co.uk