Girl Friday,
I would definately recommend checking out Stapleford, which as Flying For Fun says just a bus ride from Romford. They have a great reputation and their modular course is cheaper than some of the other FTOs. I'm training there at the moment and can't fault anything!
There are several FTOs around London and my advice would be to look around any schools that catch your eye.
Start with Stapleford at
http://www.flysfc.com/ 
Cheers,
CapCon