Holiday courses
Are you specifically wanting to fly at Dunstable or could you fly at a different location.
A year or so ago I was looking around at the different holiday courses on offer from the various gliding clubs as a way to get back in to gliding after a 10 year lay off. There was a considerable variation in what different clubs offered in terms of the amount of flying and the ratio of pupils per glider/instructor
Some also offer a guarantee that if you don't achieve a set amount of flying you will get a pro rata refund.
London Gliding club have an excellent reputation and will do a very good job of training you, but definitely worth having a shop around as it may be possible to get more for your money
David