Within 2 hours of London give you are very wide choice.
I think the Pilot Centre at Denham is hard to beat
The Pilot Centre
If you wanted to take a slightly different (cheaper) route then you could investigate learning on a TMG and then converting to SEP.
The folks at Oxfordshire Sport Flying could help with that route - Enstone in just within 2 hours of London:
Enstone Aerodrome
Or for a different type of flying (which will stand you in good stead for anything you want to go onto) try:
Tiger Club
OC619