The YHA also do summer camps.
See this web site
http://www.doit4real.co.uk/
The camps have all sorts of themes (sport, computer, activity etc)
My son who is 16 went on one last year, and it was mostly with girls, so he was well pleased.
They arrange coaches from all over the UK to the places where the camps are.
We live in Birmingham and our son got a coach from near where we live all the way to the camp.
Last year, they had a deal wherby if you had never been on one of their camps it only cost �100 but I am not sure if they are doing that this year.
And dont think they are boring. Last year he did rock climbing, canoing, caving, archery, sailing, and they had a day at a nearby theme park.
It is for people between 11 and 17, but they do split you into age groups so you will not be stuck with a load of 11 year olds.
And most of they leaders are teenagers or early 20s so that make sure it is a lot of fun.