I can recommend Firecrest Aviation at Elstree Aerodrome, I did my PPL there (passed just recently). They are a very friendly bunch who operate a fleet of Cessnas and, more importantly, have a team of good, patient instructors (they certainly needed to be patient with my antics).
The only slight down side is the aerodrome itself which is pretty crowded with bizarre circuits, not to mention the rather short and humpy r/way. Hey ho, all good experience though...