The party has said the money - which is roughly what is spent on a child's secondary education in the state sector - would be targeted at low-income families.

With fees at independent schools at about �6,000, there would be a shortfall, which the Tories say would be made up by an independent schools bursary or a business scholarship.

The details are being announced by the shadow education secretary Theresa May in a speech to the Independent Schools Association.

Conservatives want to ensure that children from less well-off backgrounds and for whom the state sector is not able to meet their needs, are able to have access to the education that is right for them.

Theresa May, shadow education secretary

The Conservatives have been looking at the idea of a replacement for the assisted places scheme for some time, but say their proposals have now been finalised.

Theresa May is telling the ISC: "Conservatives want to ensure that children from less well-off backgrounds and for whom the state sector is not able to meet their needs, are able to have access to the education that is right for them.

"Tony Blair talked this week about investing money in young people through baby bonds.

"I think that one of the best investments the government could make would be to accept the principle of opening access to schools like yours once again to children from less well-off backgrounds."

The Tories say they have drawn on proposals put forward by the Independent Schools Council, but unlike the ISC, have based their plans on the assumption that the schools system had been reorganised by a Conservative government.

Assisted places scheme

Labour is phasing out the assisted places scheme. The last children to be educated under it started at their primary or secondary schools in 1997.

There are about 19,000 children still attending independent schools under the scheme, down from a peak of about 40,000.

This week, the general secretary of the Independent Schools Council, Alistair Cooke, outlined his organisation's proposals, promising that they would be free of the problems which led to criticism of the assisted places scheme.

He said it had been criticised for concentrating high spending on a few pupils, helping only the academically talented in highly selective schools, and had been open to "abuse by middle-class parents with sharp accountants".

The independent sector's best kept secret is that many of its schools - perhaps as many as half - impose no academic admission test at all

Alistair Cooke, Independent Schools Council

Writing in the Daily Telegraph, he said the ISC's scheme differed most crucially from the assisted places scheme by not being academically selective.

"The independent sector's best kept secret is that many of its schools - perhaps as many as half - impose no academic admission test at all," he said.

The Conservatives' proposals do involve selection.

They say their scheme would target help towards low-income families who have children who are academically able or who have a special talent - for example for languages or sport.

Theresa May said the Tories would have safeguards to prevent wily middle-class parents from abusing the system.

She is telling the ISA: "I believe this system was attacked with some justification for being open to abuse by parents who were better placed to take advantage of the system.

"Under our new system there would be a more rigorous examination of capital assets and the overall financial situation of parents before any award was made."

Earlier this month, the prime minister told delegates at the annual conference of the Association of Teachers and Lecturers that he would like one day to increase spending per pupil in the state sector to the level of spending in the private sector.

The Independent Schools Council has said it is pleased the Conservatives are addressing the issue of access to independent schools.

But the organisation is critical of the Tories' commitment to the selection of applicants on abilty.

A spokesman said: "We do not believe that any scheme should be limited to children with special abilities or aptitudes. ISC schools have much to offer children of all talents and aptitudes.

"We would prefer a more far-reaching and inclusive scheme. To that end, we are pursuing our discussions all parties."