David Cameron is facing a fresh challenge to his authority with a member of his frontbench team producing new evidence showing that grammar schools dramatically improve the exam results of a whole neighbourhood.

Graham Brady, the Shadow Europe Minister and a former grammar school pupil, has passed data to The Timesshowing that GCSE results are significantly better in areas that have an element of selective education – with ethnic minority children benefiting most.

The figures show that in comprehensive areas with no selection, 42.6 per cent of GCSE pupils get 5 or more A* to C grades in subjects including English and maths. This rises to 46 per cent in partially selective areas and 49.8 per cent in wholly selective areas where all pupils take the 11 plus.

This new frontbench division will dismay both Mr Cameron and David Willetts, the Shadow Education Secretary, who unveiled further controversial policy reforms yesterday. He wants city academies to choose pupils by a range of nonacademic criteria, including race, which he hopes will halt growing segregation in some inner city areas.

Mr Cameron yesterday called critics of his refusal to bring back grammar schools “inverse class warriors”.

Mr Brady’s figures challenge a key element of Tory thinking – that pupils who fail to get into grammar schools suffer more than those who go to schools where there is no local selection. His figures show: Areas with academic selection appear to benefit ethnic minorities, and Chinese and Bangladeshi children most. Chinese students get a 82.4 per cent rating for good GCSEs in selective areas but average 61.2 per cent in comprehensive areas. Bangladeshi students get 57 per cent in selective areas but 37.9 per cent in nonselective areas. Eight out of the top ten highest-scoring local authorities in maths and seven out of ten in English are either fully selective or partially selective. Children in areas with nonselective schools are more likely to go backwards between the ages of 11 and 14, according to data released this week.

In a further challenge, Mr Brady questioned whether free school meals – the measure of poverty used by Mr Willetts – was appropriate.

He passed a letter to The Times from the headmaster of Altrincham Grammar School for Boys, who says that the educational maintenance allowance, which has a higher cutoff, provides a “truer reflection” of the profile of the school.

Mr Brady said: “These facts appear to confirm my own experiences: that selection raises the standards for everyone in both grammar and high schools in selective areas.

“I accept the party’s policy on grammar schools. But it is vitally important that policy should be developed with a full understanding of all of these facts – which might lead to the introduction of selection in other ways, including partial selection in academies and other schools.”

Professor Alan Smithers, of the University of Buckingham, said that the figures were significant. “It’s acknowledged that grammar schools work very well for children in them, but the argument against has always been that children who don’t go to the grammar achieve below what they would get in a comprehensive system. But it does look as though it is difficult to sustain the argument.”

He noted that grammar school pupils often came from more privileged backgrounds.

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