Hi! I asked a similar question a while ago and got this answer from Sunnyside:
"I really like Dario at
http://www.novopilates.co.uk
It's Clapham Junction rather than Clapham Common, but I think he's the best Pilates instructor in the area. He really cares about technique. He made me do hip bridges over and over again until I got it just right.
There are some reformer classes in Clapham, but there were too many people in the classes and the instructors didn't really care about technique. I did leave one injured.
I'd definitely go for Novo Pilates or private instruction to start with, especially if you've recently (within the year) had a baby. It's so easy to injure yourself and have to start all over again"
I really like them. Give it a try!