David Cameron stokes the row over grammar schools today with an attack on his critics’ “ideological self-indulgence” – despite warnings from Conservative MPs that activists are threatening to quit the party over the issue.

The Conservative leader promises in an article in The Times today not to be distracted from his education policy by the internal backlash. Mr Cameron writes that he is “determined to move on from a sterile debate about building a few more grammar schools”.

He argues: “Parents will not forgive any political party’s ideological self-indulgence on education, at a time when 355,000 pupils are failing to get five good GCSEs, including English and maths.”

The row over the 11-plus has rumbled since David Willetts, the Shadow Education Secretary, said last Wednesday that it “entrenches advantage”. His speech provoked a furious response within the Tory party, with Michael Howard, Mr Cameron’s predecessor as Tory leader, David Davis, the Shadow Home Secretary, and Liam Fox, the Shadow Defence Secretary, all reported to be angry at what critics said was a calculated attack on grammar schools.

The Times has learnt that Mr Willetts carried out focus group research earlier this year to test his message that there should be no return to the 11-plus. Aides insist that he and Mr Cameron were initially taken by surprise by the reaction.

The Tory leader attempted to turn the issue into a test of his leadership yesterday. In a strong attack on his opponents, he said that those wanting to build more grammar schools were delusional.

“We are debating something that we didn’t do, we weren’t going to do and even if we did do it, would have been undone,” he told a press conference. “We need to clear out of the way the argument about grammar schools. It has been a chain around our necks.”

His head-on confrontation was criticised privately by some party frontbenchers. “I’m not sure that coming out all guns blazing is [the way] to damp it down. Trying to turn this into some sort of Clause Four moment is unusually ill-advised,” said one.

Although there was no sign of a frontbench resignation last night, MPs said that local party members were preparing to quit.

Hugh Robertson, the Conservatives’ sports spokesman and MP for Faversham and Mid Kent, confirmed that he had given warning that members of his local Conservative association were threatening to leave the party in protest. A similar warning is said to have been delivered by Robert Key, Conservative MP for Salisbury, at a meeting of the Tory back-bench 1922 Committee last week.

Mr Cameron is determined not to give ground on the 11-plus but is preparing to offer an olive branch to traditional supporters by announcing plans to toughen discipline in schools.

He will call for head teachers to have greater freedom to expel unruly pupils by removing a parent’s right to appeal against a head’s decision to exclude their child.

He will also say that Ofsted inspectors should have a new remit to report on consistency of discipline policy across a school, to ensure that some teachers are not strict and others soft, leaving children confused over what is acceptable behaviour.

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