Figures revealed by Education Secretary Charles Clarke to the House of Commons show that pupil numbers in grammars have risen from 111,846 in 1993 to 150,750 this year. This is the equivalent of opening 46 new grammar schools. The 35 per cent increase has come as a surprise to grammar-school heads as well as anti-selection campaigners.

The Government claims that the main reason numbers have risen since 1997 is that eight schools were redesignated as grammars in 1998, taking the total to 164. But grammar schools have continued to expand since 1999, taking on 9,873 more students, the equivalent of 11 more schools.

Before Labour came to power, David Blunkett, then Labour’s education spokesman who went on to become Education Secretary, famously told the party’s annual conference in 1995: “Read my lips. No selection, either by examination or interview under a Labour government.”

Aides later said that Mr Blunkett had meant to say “no more selection”.

Margaret Tulloch, of the Campaign for State Education, said the new figures clearly undermined the minister’s pledge.

“The original promise was no selection, then it became no more selection,” she said. “Even that has not happened because of the way grammar schools have expanded. Selection is not a marginal issue, it affects a large number of children.”

Mrs Tulloch said the increase in selection was even greater than the figures suggested because of the introduction of specialist schools.

Around 100 of the 1,686 specialist schools are believed to be using powers to select up to one-tenth of their students by aptitude.

When Labour came to power it decided not to abolish grammar schools, instead setting up a complicated balloting system for parents to vote them out of existence. Since then only one ballot has been held, in Ripon, North Yorkshire, where parents voted to retain their local grammar school.

David Miliband, minister for school standards, told anti-selection campaigners this month that he would vote against grammar schools if he were a parent in an authority where a ballot was held.

Brian Wills-Pope, chairman of the National Grammar Schools Association, said the figures proved that grammars remained extremely popular despite opposition from Labour ministers. Their expansion was a result of “parent pressure”.

The percentage of secondary pupils in grammar schools was 3.l per cent in 1983, 3.8 per cent in 1993, 4.2 per cent in 1997, 4.5 per cent in 2000, and 4.6 per cent in 2004. While grammar-school pupil numbers rose by 35 per cent over the past decade, they dropped by 5 per cent between 1983 and 1993 under a Tory government.

A Department for Education and Skills spokeswoman said the proportion of pupils in grammars had risen since 2000 because of increased capacity at the schools, but stressed that the rise was only minimal.