Some earlier discussions about flight schools near London covered this question:
Flying school for PPL around London (~2-hour driving radius)
Flying clubs around London
Stapleford PPL training There's more in here about Stapleford than Redhill, but both are mentioned in these threads. I'm sure someone else will turn up with more up to date information. All I can add is that I enjoyed the cafe at Stapleford the one time I was there
