Weight loss club for teens

[BusyBusyBusy1]

My 12 yo is overweight and getting more so - I can see that if he carries on with his current eating habits he could easily end up in the obese category (he is at the top of the weight range for his age but of average height). We have tried simple measures, been to an NHS healthy choices club, without any real effect. I think he might benefit from a weight loss club - like WW or SW, to help him learn how to eat healthily and loose a bit of weight (or just not gain any weight so his height can catch up). A weekly meeting might be better than online check-in given that there will be a lot to take in. My GP didn't know of anything that might suit him, does anyone have any advice or ideas? We are based in Camden, London
Thanks!!

SW has a plan for 11-15 year olds that is great. They just need to be accompanied by an adult. It's done with the approval of a gp or school nurse so you know it's safe too.

Also don't know if you have tried this but my snack rules are fruit, veg and dairy. Nothing else.

Sweets are for Saturday only.

Drinking water throughout the day is a must.

Is he over eating or could it be his thyroid?

Thanks for the tips so far. It is over eating I am afraid Quitelikely, I find him foraging in the kitchen in the evening and even though we don't keep sweets, chocolates biscuits in the house, he manages to work his way through things like breakfast cereal, waffles etc. Snack rules sound like a good idea but he never (and I mean never) eats veg or fruit. However he loves cheese and milk so that could work. I would love to cut the sweets down to Saturday only but so far have only got it down to one small (30G or less) chocolate bar a day for each child after school. It is hard to go to no treat a day because this works fine for his siblings - they are slim and able to say no when they are full. He has a different appetite to them.
Will look into SW - it sounds perfect.

Overweight in teen is more and more common.
To get to the bottom of this problem, you need to improve his metabolism and digestion. There are ways of doing so. The basic knowledge is to understand that kids need to eat cooked/balanced food. If they are not hungry - they will less and less require snacks. Teens are hungry of energy (its not the same as calories); and this you can achieve only by preparing nice, cooked food at home (at least breakfast and dinner).
There will be a workshop 'Healing Food for Children' in January 2015 in Fulham, where I will be explaining what works and what does not if we want to help our teens to loose weight.