I live in the South east also (Sidcup), and deciced to learn at Biggin Hill, as it was the closest airfield, and it had a hard runway. As others have said, the landing fees are quite expensive (£18 I think), but you do get to learn in a full ATC environment, which helps your radio skills develope quite quickly.
I thoroughly enjoyed my training, and I'm sure you will too, whereever you decide.