My ortho is Paul Ward at Thames Orthodontics - he is brilliant and teaches other orthos (I've been the subject of one of his lessons before!) He specialises in Lingual braces (I have upper lingual, lower ceramic)
The first consultation is also free - and from that they'll give you an estimate and tell you how long they expect treatment to be.
The nearest train station is Fulwell which is out of the way of Central London but I'd definitely recommend if you can get there - I know some people travel a long way to see him.
Good Luck, let me know if you need more specific details