Just had to rave about Ashley Green (not the actress for Twighlight by the way). He teaches the most fun Zumba class at The Bedford in Balham on Saturday morning and Mon and Wed eve, i come out grinning from ear to ear. And he also does personal training sessions at a reasonable rate. More importantly he's a really nice guy.
http://www.ashleygreenfitness.com/
http://www.zumba-ashleygreen.com/#!home/mainPage