We teach it at my college, and students like it as it helps them to be more rounded without having to do the IB.
They have to do their core 'A' levels (Any three they choose from any exam board)
Then they must do a further 'AS Level' (For this they can choose from General Studies, Critical Thinking or Citizenship.
Then they must do an extended project. This can be on anything they like - I know current students doing this ranging from exploring gay rights, alternatives to the British education system to more arty projects. I think it tends to be about a 5,000 word essay or mini dissertation. However, it does not have to be an essay - they can do it in another format such as a short film etc.
Then they must do 100 hours. This must be made up from 2 of the three categories which are personal development, community service and something else I can't remember at the moment. It sounds a lot, but this does include paid work, any 'extra' courses they do or if they help out with the Brownies or anything like that.
The benefits of this is that will the exception of the 100 hours, everything else is also credited individually so, if it gets a bit much for them, they can drop the AQA BAC and still get points for the 'A' levels, and even the extended project carries UCAS points (equiv points to an AS, depending on the grade they are awarded). I have done this from memory so please don't quote me, but I think it is correct. HTH