A Labour government will strip private schools of valuable tax breaks worth hundreds of millions of pounds unless they do more to help the state sector, shadow education secretary Tristram Hunt is warning.

In a keynote speech today, Mr Hunt will tell private schools in England they will lose business rates relief - worth an estimated £700 million over the course of a parliament - unless they are prepared to meet minimum standards of partnership with their state counterparts.

He will say that a Labour government will legislate to ensure the schools only qualify for this 'subsidy' if they pass a new 'schools partnership standard'.

Under this system, private schools would be required to provide teachers in specialist subjects to state schools, and to share expertise to help state school pupils get into top universities.

The will also have to run joint extra-curricular programmes with state schools as equal partners so that children from the state and private sectors mix together and learn from each other.

Mr Hunt, who was himself privately educated, will point to figures showing that just 3% of private schools sponsor an academy, while a further 5% loan teaching staff to state schools, and a third share facilities.

'The only possible answer to whether they earn their £700 million subsidy is a resounding and unequivocal 'no',' he will say.

'Over the last few years we have seen the limitations of asking private schools politely. So the next government will say to them 'Step up and play your part. Earn your keep. Because the time you could expect something for nothing is over'.'

'I realise that to some this may seem an unnecessarily tough test. But that is not because I want to penalise private education but because I want to make sure we break down the barriers holding Britain back.'

The move is likely to provoke a renewed row between Labour and the private schools sector. Barnaby Lenon, the chairman of the Independent Schools Council, said removing business rate relief would be 'a very ineffective tool' to improve social mobility.

'Independent schools are committed to helping widen access to their schools and to improving social mobility. Already 90% of our schools are involved in meaningful and effective partnerships with state schools and their local communities,' he told the Daily Telegraph.