Bernard Jenkin, who was Tory deputy chairman until being sacked last November, described the row over schools as the "first skid mark" of Mr Cameron's leadership and said he was glad that the party was now saying areas with selective systems could open new grammars.

Meanwhile, former Cabinet minister David Mellor warned that it was "foolish" for an Old Etonian like Mr Cameron to be seen to want to "pull up the ladder of opportunity from ordinary folk".

He warned Mr Cameron not to invite comparisons with 1960s Conservative leader Harold Macmillan, whose Government was packed with old Etonians and who was widely seen as being out of touch with ordinary voters.

Shadow education secretary David Willetts' announcement last month that the Tories were dropping their commitment to more selective state schools sparked the biggest internal battle of Mr Cameron's 18 months as leader, provoking the first resignation from his frontbench team when Europe spokesman Graham Brady quit on Tuesday.

On Thursday Labour accused Mr Cameron of caving in to pressure from his party and performing a U-turn after shadow attorney general Dominic Grieve voiced his support for the opening of more grammar schools in his Buckinghamshire constituency.

Mr Willetts insisted Mr Grieve was not at odds with the party's line, as it was accepted that in areas which already have selective schools, new grammars may have to be opened in response to demographic pressure.

But Education Secretary Alan Johnson said: "After two weeks of pressure from his unchanged and unreformed party, David Cameron has caved in. This is abject surrender from David Cameron, who said only last week: 'I lead. I don't follow my party, I lead them.'"

Mr Jenkin indicated that he too would like to see new grammar schools open in his Essex North constituency. Mr Jenkin said: "I have grammar schools in my constituency. I'm a supporter of grammar schools. I'm glad that the party is now saying that in areas where there are grammar schools the authorities may apply to build new grammar schools to deal with larger populations."

Mr Jenkin said he believed the Tories' education policy would "evolve" between now and the General Election, expected in 2009 or 2010, and suggested that Mr Cameron may drop his support for Tony Blair's network of non-selective city academies. "The election is still some way away and policies will evolve," he said.