I know your post is 1 year old but maybe you are still looking for a lovely local adult ballet class?
I posted this on here two days ago (see link). viewtopic.php?f=47&t=94726
I am one of the mummy students in that class and am really loving it. It's at Freshground, Battersea Rise, very close to Northcote Rd and Clapham Junction.
Don't hesitate to send me a private message if you would like to know more.