Where we are, there has been a move towards starting in Yr9. Some subjects didn't actually teach the specification until part way through yr9 in the early days, but having found the content is so heavy to get through, now do start on the actual GCSE right from the start.
It has been noticeable that the selective schools (Independnet and state) are doing 3 year GCSEs and gradually the Comps are moving in that direction too. Some has moved that way after a poor set of GCSE results or disappointing Ofsted.
Isn't one thing all schools are very interested in now, this interleaving thing - where you don't just plough through all the new material and then revise it all at the end, but teach new material and keep re-visiting old topics all the way through - someone mentioned it about maths upthread. I thought this was the big thing now in all subjects and meant to really get the information or skills into lomg term memory. Presumably, if you spend 20% (guessing here) of your time re-visiting previous topics,mig takes longer to complete a course, so 3 years might help.
I'm sure schools do it because they hope it will boost GCSE performance and league tables....this might be seen as vital with more content heavy courses now, although I can see that if a mix of Btecs and GCSEs are taught it might not work so well if Btecs really don't take more than 2 years.
Cynically, I also think it has allowed some schools to save money - by teaching less classes the artistic subjects which might need smaller classes, and driving students towards fewer GCSEs (more periods for maths and English etc) they don't need to many teachers of the practical subjects and this has also contributed to the closing down of some subjects. I think some of these decisions have been led by the tight budgets not educational reasons.
Personally I think 3 year GCSE is fine, but definitely good to include a humanity, a language and in most cases a practical subject too, to maintain breadth. Some schools often some kind of non-examined lesson a week too where they can pick for a wide range of topics and cover something they're not doing at GCSE, like an art module etc, which can mean they don't totally lose the things they don't do for GCSE - but I think this tends to be the huge schools that can staff such things.