I am on my way to better fitness thanks to House of Yoga on the Upper Richmond Road. They offer Hot Yoga and it is a combination of muscle toning and cardio so I love the combination. The instructors are all experienced and you can really attend any class and do the positions which suit your level best. I am slowly building holding my poses and stretches and you feel great after an hour of doing it. If you hate sweating in a hot room this isn't for you, but you truly feel fantastic after the class!
If you prefer the more traditional yoga class, where you get the same workout without the heated room, you can't beat Yoga Mama at The Putney Clinic of Physical Therapy. Anyone who has attended one of Cherie's classes, knows she is the best in Putney. http://www.yogamama.co.uk/