Free schools? How free? Free from local authority, sure. But not free from control of central government. After all, if you want the cash to start one up, you have to adhere to the ethos that selection is not allowed.
It this kabosh on academic selection that greatly halts excellence in education for the young and especially those who live in poor areas. Kids who are academically minded should have a school they can attend that is about academic rigour. Those who aren't academic should be able to develop vocational skills at a young age instead of being pressed into system of education that is ill-suited for them.
If free schools were allowed to be set up in such a way, that would be true decentralisation from government. Alas, comprehensive hell goes on under another guise.