The Prime Minister is to make the extension of self-governing schools a manifesto commitment. He believes the move will be popular with parents and will highlight differences between the three parties’ education policies.

It has long been an ambition of Mr Major’s to make all schools grant-maintained. With one in five pupils taught in GM secondaries, he will play on parental fears for the future of their school under Labour .

Former education secretary John Patten’s bids to force all secondary schools to opt out were rejected because it would have undermined the principle of parental choice, a cornerstone of the GM legislation.

The Tory manifesto group now believes it could avoid that problem by telling all secondary schools to ballot. The law requires schools to consider ballots, but Tories believe many decide not to on the nod.

The compulsory ballot, which would almost certainly require legislation, has support from all levels within the Conservative party who have blamed Labour and Liberal Democrat local authorities for persuading schools not to opt out. The proposal is likely to be included in the party manifesto.

There are just 1,158 GM schools out of a total 26,000 primaries and secondaries in England and Wales. Between September 1995 and December 1996, 49 secondary schools have held ballots with 22 voting yes. The impending general election has made schools wary about becoming GM in case of a Labour government. If the Conservatives win, they believe many schools will vote yes.

Two years ago Mr Major told the Grant Maintained Schools Foundation his ambition was that all state schools should become self-governing. The idea was to provide a fast-track to GM for church schools, but this was opposed by the bishops and had to be dropped.

Since then he has sought to make GM status more attractive by giving the schools more power and making it easier for them to introduce selection. The Education Bill, now being considered by Parliament, will allow them greater selection and the option of opening nurseries and sixth forms without permission.

It is understood the compulsory secondary ballot will pave the way for one for primary schools, at a later date. This will give the Funding Agency for Schools time to prepare itself to take on the 21,000 primaries. At present, under 4 per cent of primary pupils are in GM schools. The FAS and the Department for Education and Employment are already working on a national funding formula for schools.

All party leaders claim education is their top pririoty, but increasingly there is a consensus on the national curriculum and testing, inspections and discipline. The GM issue divides parties. The Liberal Democrats say they will return GM schools to local authority control. Under Labour, GM schools are likely to become foundation schools, with a similar governing body, but a stronger role for parents and two LEA governors.

Other expected Conservative manifesto pledges are more grammar schools and the expansion of popular schools.