At least 100 leading private schools will be expected to sponsor academies or set up free schools if the Conservative Party wins the election.
The Tory manifesto, launched today, says the party will "keep open the option of changing the tax status of independent schools if progress is not made".
The election pledge follows the government's Green Paper, which said that the best independent schools would be expected to sponsor state schools and offer funded places – or face losing benefits associated with charitable status.
The consultation paper, entitled Schools That Work for Everyone, proposed that "independent schools with the capacity and capability" should sponsor an academy or set up a new free school – or offer a certain proportion of places as fully funded bursaries to those who are unable to pay fees.
Threat over charitable status
Today's manifesto does not mention bursaries, but it does set out the number of independent schools that would be expected to sponsor academies or set up free schools.
It says: "We will work with the Independent Schools Council to ensure that at least 100 leading independent schools become involved in academy sponsorship or the founding of free schools in the state system, keeping open the option of changing the tax status of independent schools if progress is not made."
In recent years, a number of top private schools have come across difficulties when trying to improve the academies they sponsor.
Wellington College in Berkshire initially struggled to raise standards at its state academy, The Wellington Academy in Wiltshire, and the first headteacher left following a batch of poor GCSE results.
And Dulwich College in south London stepped down from its role at the troubled Isle of Sheppey Academy in Kent in January 2013 to make way for the Oasis academy chain, after admitting that its staff were not equipped to help pupils at the state comprehensive.