A Labour government would introduce a requirement for private schools to draw up agreements setting out how they would support their state counterparts or face losing their business rate relief.
In a speech today, Tristram Hunt, the shadow education secretary, will say that his party would aim to break down the "corrosive divide" in education beween state and private schools, most of which are registered charities.
This would be done by making the £700m that Labour says private schools would receive in business rate relief over the next five-year parliamentary term conditional on them meeting minimum standards of partnership with the state sector.
Hunt will say at Walthamstow Academy in north London that his party would amend the Local Government Act 1988 to make the relief payable only when fee-charging schools met a new "schools partnership standard".
This would require them to provide qualified teachers in specialist subjects to state schools, share expertise to help state school students get into top universities and run joint extra-curricular programmes with state schools as equal partners "so children can mix and sectors can learn from each other", he will say.
"If we are to prosper as a country, we need to be a more equal country," Hunt will say. "If we are to make the most of the wealth of talent that exists in every school and every community, we need to give every child a chance.
"And if we are to be a country that works for most people, we need to break down the divisions in our school system with concerted, collaborative and coordinated action from the entire English educational landscape, including the private sector."
Hunt will also say: "It baffles me that we can have private schools loaning a sports pitch to the local comprehensive once or twice a year yet completely refusing to play them at football, or opening up their halls and amphitheatres yet are unwilling to engage in a debating competition."
Hunt has also indicated that a Labour government would be unable to threaten the charitable status of fee-charging schools after the Independent Schools Council, which represents more than 1,200 fee-charging schools, challenged the Charity Commission’s guidance on what the schools must do to meet the public benefit requirement.
Writing in The Guardian newspaper today, Hunt said that Labour’s attempts to require fee-charging schools to do more to keep their charitable status "collapsed in the law courts".
The Charity Commission produced much looser guidance for trustees of fee-charging charities as to how they should meet their public benefit requirements after the ISC challenge.
Responding to Labour’s plans, Barnaby Lenon, chair of the ISC, said today that clawing back business rate relief from independent schools "seems a very ineffective tool to improve social mobility in any meaningful way".
He said: "Independent schools are committed to helping widen access to their schools and to improving social mobility. Already 90 per cent of our schools are involved in meaningful and effective partnerships with state schools and their local communities.
"Independent schools generate £4.7bn in tax and save the taxpayer a further £4bn, equivalent to building 460 schools, by educating children out of the state school sector. To subject independent schools to one-size-fits-all regulations does not take into account the diverse nature of our sector – many are small local schools."