Tony Blair has defended his plans for student top-up fees, arguing that they will allow an expansion in higher education without burdening taxpayers.
Students will lobby Parliament on Wednesday
The prime minister insisted the plans were fairer than the status quo.
But, speaking in the Commons, Tory leader Michael Howard accused Mr Blair of breaking election manifesto pledges.
Mr Blair earlier met backbench Labour MPs, many of whom argue the plans will discourage the less well off from going to university.
Some 149 Labour MPs have signed a Commons motion voicing concern about the plans.
Fears centre on allowing different universities to charge different sums - up to £3,000 a year.
That would almost triple the current tuition fees in England, but the fees would be repaid after graduation rather than up front.
Education Secretary Charles Clarke said a Commons vote on the plans had been delayed until the New Year to allow time to address colleagues' concerns.
"In my opinion, we would have carried it before Christmas and we will carry it after Christmas," he told the BBC.
Mr Blair reportedly faced "frank questions" from backbenchers during the meeting in the Commons.
At prime minister's questions in the Commons, Mr Blair said Tory plans to scrap the fees would deny access to university to 460,000 young people.
But Mr Howard said: "Don't you realise quite how ridiculous you are beginning to look? If you won't listen to the people, why on earth should anyone listen to you?"
Clarke says it is "grossly unfair" to charge all students the same
He asked Mr Blair if he would scrap the plans if a majority of people asked him to in Labour's "big conversation".
The prime minister said: "Of course we will always listen to what people say. But what people are saying is we need to fund lifelong education."
As the prime minister attacked Tory plans, Mr Howard said that as a grammar school boy he would not take lessons from a public school boy on helping less privileged students get to university.
In heated exchanges, Mr Blair countered: "There are lots of people in this country who went neither to grammar schools, nor to public schools.
"Surely their interest is to be able to go to university and have the places available?"
Asked by Lib Dem leader Charles Kennedy whether the forthcoming vote on top-up fees amounted to a vote of confidence in his leadership, Mr Blair said: "Of course it is important for the government - all these votes are important to the government."
He has already admitted his authority is "on the line" over the vote.
And on Wednesday he promised to publish the education department's studies of the three other options for student funding - a graduate tax, a flat rate charge and raising income tax.
In the run-up to Christmas, Mr Clarke is to hold three meetings with Labour MPs to explain why he has rejected the alternatives to variable fees.
The Higher Education Bill will be published as soon as MPs return from their Christmas break.
Students are also stepping up their opposition to the plans with a national lobby of Parliament.
Between 100 and 200 people joined a The National Union of Students lobby of MPs at Westminster.
Mandy Telford, NUS president, told BBC News Online: "Rather than protesting, we are actually speaking to MPs so they are going to hear from their own constituents about how upset they are with the government's plans."
In a Commons debate on the Queen's Speech, Mr Clarke insisted variable fees were fair.
And he said there would be bursaries to ensure access was down to talent, not the ability to pay.
As a result of the proposals, Cambridge University had suggested one in three students could get £4,000 a year in bursaries, he said.
Earlier, Mr Clarke laid out what was at stake on the fees issue.
"This proposal is at the heart of building a competitive economy in a very competitive world which must be based on investing in the skills and talents of our people," he told BBC Radio 4's Today programme.
"If we fail to get it through, our authority in identifying that challenge is very substantially weakened."
Ministers point to the backing of university chiefs, who say they need to fill an £8bn funding shortfall.
But the Commons debate saw more criticism, with ministerial aide Colin Pickthall saying the plans were "neither desirable
The MP would have to resign as the foreign secretary's aide if he joined the rebel vote.