If you're looking for a mum's class, there's Buggyfit and PowerPramming on Tooting Common. I think PowerPramming is becoming Trainhappy now.
For regular classes, I think OneElement, Swift, and British Military Fitness all hold classes on Tooting Common and there are probably even others. These all offer free trials too. Websites below.http://www.buggyfit.co.ukhttp://www.trainhappy.co.ukhttp://www.one-element.co.ukhttp://www.swiftfitnessgroup.co.ukhttp://www.britmilfit.com
I've tried all of the above except Swift. The buggy ones aren't quite as good of a work-out as the others obviously, but quite good socially to meet other mums.