Ann Widdecombe is threatening to reopen Tory policy divisions over Section 28, the legislation banning the "promotion" of homosexuality by local education authorities.
Some senior Conservatives had hoped the issue could be allowed to die quietly next week during the committee stage of the Local Government Bill. But the former shadow Home Secretary has made clear that she will mount a "freelance operation" from the back benches if the leadership failed to press the issue at report stage.
Her warning is likely to persuade David Davis, the shadow Deputy Prime Minister, to table a fresh amendment to the Government's Bill giving parents a direct say over sex education taught in schools.
Iain Duncan Smith, the Tory leader, and Mr Davis agreed earlier this year to back a new policy on Section 28 that would protect children without stigmatising homosexuals. The law was introduced by the former prime minister Margaret Thatcher.
The Tory alternative will compel headteachers to ballot all parents if 5 per cent object to the content of the materials used for sex education. Bill Cash, the shadow Attorney General, has spent recent days finalising the amendment.
John Bercow, Tory MP for Buckingham, who resigned from the Shadow Cabinet over gay adoption, has been joined by Michael Portillo and other liberal backbenchers in signing a cross-party amendment aiming to abolish Section 28.
Several Tories believe that the whole controversy can only do damage to the party. "We walk straight into Labour's trap if we get too strident about this," one said. As a result, Mr Davis has been under pressure to table his compromise amendment only in committee, where it would be defeated by the Labour majority, and not bring it back to the floor of the Commons for the report stage.
But Ms Widdecombe said: "I hope we are sensible and bring it to the floor of the House. If we don't, I and others will conduct a freelance operation to make sure it does."
Meanwhile, Mr Duncan Smith dismissed reports of a leadership challenge by Mr Davis. Echoing a report in The Independent last year, a newspaper said Mr Davis was prepared to fight against Kenneth Clarke if Mr Duncan Smith should step down. Mr Duncan Smith said: "It's absolute rubbish. The reports are simply rubbish – it's all been dropped now."
Mr Davis said in a statement: "I have made it clear before that under no circumstances will I mount a challenge to Iain Duncan Smith. I believe that he is doing a first-rate job in leading the Conservative Party. I firmly believe that Iain will lead the party into the next general election and that he will win it."