There is no evidence so far that academies are driving improvement in English schools, according to the cross-party parliamentary education select committee.

But it says the academy programme has led to greater competition which has challenged many maintained schools to improve and encouraged local authorities to intervene more effectively when they underperform.

In its report on academies and free schools the committee says Ofsted must be given full powers to inspect academy chains and calls for much more transparency on what really works.

It argues that the autonomous state schools can be very successful but the government needs to be much more open about the scheme and improve supervision.

It says some academy chains have proved very effective at raising attainment, while others achieve worse outcomes than comparable mainstream schools.

Graham Stuart, the committee's chair, said: 'Current evidence does not prove that academies raise standards overall or for disadvantaged children.

'It is clear though that academisation has led to greater competition, challenging many maintained schools to improve and incentivising local authorities to develop speedier and more effective interventions in underperforming schools.'