A source close to Mrs Shephard this week dismissed the GM lobby as unrealistic, claiming that many schools want to keep their links with the local authority.

In what appears to be an important policy shift, the source praised the local authority structure and said compulsory GM status could never be a cure all: “What good would it have done The Ridings school to have been grant-maintained? Would it have changed over night? I doubt it.”

The GM lobby are particularly disappointed that the manifesto makes no commitment to speed up opting out as they know they have the support of the Prime Minister and several senior Cabinet members for a further expansion. Instead the manifesto proposes to create “locally-maintained schools”, giving council-run schools a greater proportion of their budget and freedom over admissions.

Mr Major will make grammar schools, but not GM schools, an important election issue. In an appeal to parents, an attempt to put “clear blue water” between the political parties, Mr Major is expected to announce incentives for comprehensive schools to become grammars.

“We will encourage more schools to become grant maintained and will allow grant-maintained schools to be set up where there is sufficient local demand,” says the manifesto.

“We will give all grant-maintained schools greater freedoms to expand and to select their pupils.”

Pauline Latham, chairman of the Grant Maintained Schools Advisory Committee, believes this does not go far enough. She said she was surprised and disappointed the Conservative party had not taken its commitment to the expansion of GM schools any further.

She had been pressing for a number of measures, either for a requirement for all secondary schools to ballot to become GM or a “reverse ballot” where schools would have to vote to stay under LEA control.

There are 1,188 GM schools. Since the autumn term there have been only 53 ballots, with 35 schools voting yes to GM status. Mrs Shephard believes many schools are not ready to become grant-maintained.

And while she has been critical of a number of LEAs, for example Islington, Southwark and Tower Hamlets, she believes many others provide a good structure and important services for schools. The Education Secretary started her political career as a Norfolk councillor, and was chair of the council’s education and social services committees.

Malcolm Thornton, chairman of the Education Select Committee, was not involved in writing the manifesto, but he believes the right tone has been set: “My view is that GM status should be evolutionary rather than revolutionary. It is right that there are parental ballots and other checks and balances. The continuing debate should be about the role of the LEA. While schools welcome delegation, many, particularly primary schools, want to retain support from the centre. ”

Conservative sources suggested that making GM status compulsory would undermine its success. “You would be taking away the principle of choice. The only way you could make all schools grant-maintained is in effect by force.

“Not all schools would want to break the link with LEAs. LEAs are not necessarily wholly bad, particularly if they do properly those things which they ought to do. There are lots of them that don’t, of course - Islington, Tower Hamlets and Calderdale for example.”

The Route to Success, a Grant Maintained Schools Foundation booklet, claims GM schools do better than other state schools. According to the 1996 performance tables, 20 of the best-performing 40 comprehensives are GM. It says a third of GM schools have increased staffing levels, 82 per cent spend more on books and equipment, and GM schools are turning away from their LEA to provide services.