Kbab,
Kenly: on top of a hill, small traingle of airspace where they can go up, but not much else. They have a T-21 though... You can got to it by train, and I cycled up the hill
Booker: aerotow only = expensive. Dunno how easy it is to get to. Mainly thermal
Dunstable: train to Luton, cycle from there. Has a ridge, winch and a/t. Seems good, but known as a soaring centre (in more ways than one)
Halton: RAFGSA difficult for civillians to break into, unless you can offer the RAFGSA something they want; are you an aircraft engineer, instructor, have a 2 seater they can also use?
If you're willing to undertake a longer journey, try Lasham. Nearest station Alton, nd a 4 mile ride from there. Reputation speaks for itself...
I wish you well; I'm in the same situation (learnt to glide, not drive, and live in London)