Briefings to the Daily Telegraph and Daily Mail by the party’s top spin doctor Peter Mandelson the day before Tony Blair outlined his new vision for comprehensive schools reached the front pages.

Mr Blair, they said, was jettisoning 30 years of Labour education dogma by ending mixed-ability teaching in schools. The phrase “Equality must not become the enemy of quality” - part of his speech last week to Didcot girls school in Oxfordshire - was seized on as an attack by Labour on the comprehensive ideal.

“Mixed-ability teaching is for some people as much of an ideology as the principle of comprehensive admission itself,” said Mr Blair. “Mixed-ability teaching may have a role . . . but it is a means not an end. If it works for a given purpose, it should be adopted. If not, other strategies should be sought.”

The line promoted in off-the-record briefings was that Mr Blair was willing to discard a cornerstone of Labour education policy in an attempt to win over Tory voters.

In his speech he said a Labour government would start with a general policy in favour of grouping by ability and hinted that he was prepared to take strong action to push it further forward.

He referred to “policy levers” including: using Grants for Education Support and Training money; asking the Office for Standards in Education to look at schools’ policies on grouping; an evaluation by the Teacher Training Agency; and promotion of the method by a new grade of advanced skills teacher.

His message mirrored the speech delivered by David Blunkett, the shadow education spokesman, to the National Association of Head Teachers annual conference which was also tougher in the selling to delegates than the telling.

On the day of his address to the NAHT, Mr Blunkett preached back to basics in the classroom in an article for the Daily Mail.

Closer inspection of the nation’s schools, however, shows mixed-ability teaching to be a false Aunt Sally for Tony Blair to knock down. The vast majority of schools do not practice it above Year 7. Setting and grouping, as espoused as a new approach by the Labour leader, are already commonplace.

Richard Pring, professor of educational studies at Oxford University, said: “It seems as though there is a funny game going on and it is far from where the action is - in schools. The idea that there is monolithic support for mixed-ability teaching is a myth.”

Just last month the biggest-ever survey of comprehensive schools revealed setting and streaming were used increasingly with older pupils.

The study, of 1,560 schools and colleges, disclosed that mixed-ability teaching was used for all subjects in Year 7 in just over half the schools surveyed but only 17 per cent used it in Year 8.

By Year 10 the vast majority had abandoned mixed-ability teaching for all subjects, said the authors of the survey, Caroline Benn and Clyde Chitty. Overall just 3 per cent operated mixed-ability classes for all pupils in all subjects.

Benn and Chitty believed mixed-ability teaching still had many advantages and could be advocated for its positive social effects.

This week a Coventry community technology college which uses 100 per cent mixed-ability teaching won glowing praise from the Office for Standards in Education and an endorsement from David Blunkett, the shadow education secretary, who includes in his team Estelle Morris, a former teacher at the school, Sidney Stringer.

Ian Kershaw, headteacher, reacted angrily to Tony Blair’s speech: “It is not the job of the politicians to determine what are the best methods of teaching. ”

The detail of the speech gives Tony Blair an escape route. “It is not, of course, up to central Government to prescribe classroom organisation in 25,000 schools,” he said. “Professional judgment according to local circumstance is important.”

But the party managers made sure their message was conveyed loud and clear.

Mr Blair said Labour would not conduct a vendetta against grammar schools and it would continue to allow church schools to interview parents about their religious convictions. It would increase delegation to schools and give parents a stronger voice on governing bodies and local authority education committees and expects LEAs and schools to agree on admissions .

The education Establishment was not impressed by Mr Blair’s pronouncement. Graham Lane, chair of the Council of Local Education Authorities and education chair of the Association of Metropolitan Authorities, said: “Some of the people who are advising him don’t know what they are talking about.”

Mr Blunkett has also been criticised for ignoring a letter from Paul Black, emeritus professor in science education, and his staff at King’s College London, which set out evidence against setting, saying it is socially divisive - working-class pupils are shown to under-perform - and overall performance is lower. The letter said that while grouping was easier for teachers and popular with parents it is not necessarily the best method for children. “We sent him the letter in March but have not even received an acknowledgement,” said Professor Margaret Brown of King’s.

The National Association of Schoolmasters Union of Women Teachers is also concerned that grouping may pave the way for selection, particularly when pupils come to choose between academic and vocational pathways.