A Tory MP who quit the frontbenches in the row over the party's policy on grammar schools has said its stance was "badly thought-out" and "absurd".
Mr Brady is a former grammar school pupil himself
Graham Brady said the party was picking a fight with ordinary families over the ending of its support for new grammars.
But Tory leader David Cameron warned the party risks being "marooned" in the past unless it embraces change.
He will reportedly attempt to face down rebels on Tuesday by pledging to step up the pace of modernisation.
According to the Observer, Mr Cameron will use a speech to British Muslims - at a conference organised by Downing Street - to assert his authority over the party.
Writing in the Sunday Times, Mr Cameron said: "Modernity matters because if we allow ourselves to be marooned on the wrong side of social and cultural change, the result is simply irrelevance and opposition."
He added: "When the dust has settled on the grammar school debate it will be equally clear that our distinctive approach - more setting in schools, head teachers' control over discipline and a big expansion in opportunities for new schools to open - is robust."
It comes amid further evidence of the scale of the grassroots revolt against Mr Cameron's education policy.
Before shadow education Secretary David Willetts' climbdown on Thursday, dozens of councillors in areas with grammar schools had threatened to stand as independents at the next election, according to the Sunday Times.
In what opponents dubbed a "humiliating U-turn," Mr Willetts said a Tory government would consider opening new grammars in areas which already had them, if population changes justified it.
A survey by the ConservativeHome.com website of 1,294 Tory members suggested that Mr Willetts' net satisfaction rating among the party grassroots has dropped from +37% before the row to -24%, while Mr Cameron's has fallen from +49% at the end of April to +22%.
Tim Montgomerie of ConservativeHome said Tories "are unhappy with the grammar schools policy but also at the way the whole affair has been handled".
Mr Brady, who resigned as Europe spokesman on Tuesday, said the grammars row could have been avoided if the party leadership had been more open before Mr Willetts made his original policy announcement.
He told Sky News: "Within the parliamentary party if we had a discussion about these ideas before David Willetts made his speech, we would have avoided the whole of this unfortunate row going on."
The ex-frontbencher continued his high-profile assault on Mr Cameron's policy in an article for the News of the World.
He called on Mr Cameron to reverse the decision and allow new grammars if parents want them.
The Altrincham and Sale West MP wrote: "First, accept it's absurd to claim grammar schools stop kids from poor families getting on in life.
"Second, make it clear that a Conservative government will listen. We don't need to promise 'a grammar school in every town', but we should make it clear that if people want one we won't stand in their way."
Before quitting, Mr Brady was reprimanded by the Conservative Party's chief whip and told to stick to his Europe brief.
But since then others, including shadow attorney general Dominic Grieve, have also defended grammar schools.
Mr Brady, a former grammar school pupil himself, accused the party leadership of trying to close down the debate.
He said: "Last week I was told if I wanted to keep my job I had better shut up about education.
"But I decided it was more important to tell the truth about something I passionately believe in."
Meanwhile, a Sunday Telegraph poll of 1,014 people suggests voters believe Gordon Brown would make a better premier than David Cameron.
But the Tories keep a five-point lead over Labour in the ICM poll.
And Mr Cameron was thought to have the best policies for schools and the NHS, according to the poll carried out on 30 and 31 May.
Mr Brown was seen best on the economy, tax, and the so-called war on terror.
He was rated to make a better premier by 45%, against 43% for Mr Cameron and the more competent by 54%, compared with 29% for the Tory leader.