Tony Blair has been warned by a former senior whip that "civil war" could break out in the party if Labour MPs feel they are being ignored.
Mr Blair suffered defeat over plans for holding terror suspects
Ex-deputy chief whip George Mudie, MP for Leeds East, said the number of people threatening to rebel on education reforms "scared" him.
Ex-minister Frank Dobson predicted up to 100 Labour MPs would join a revolt.
Meanwhile, Culture Secretary Tessa Jowell said backbenchers had a duty to back the government's reforms.
Mr Mudie, who voted against the government on Wednesday over the detention of terror suspects, urged ministers to respond to rebels' concerns.
He told BBC Radio 4's World This Weekend programme: "Unless we all calm down, take a deep breath and reconsider how we are all acting, I can see the next four years being civil war and Tory government after four years, and whoever is prime minister is going to have a party that is probably unmanageable."
Warning government whips against strong-arm tactics he said: "If somebody is reaching automatically for the stick, that is the worst thing that could happen.
"We have got to get the Parliamentary Labour Party coming together again and trying to make everybody feel they are involved, they are being listened to and what is being said is being acted upon."
He added: "I can tell you, just from speaking to colleagues, the numbers of people who said 'I am going with them on terrorism, but he has no chance on education' scares me, because it will mean disaster."
Mr Dobson estimated that the 49-strong ranks of Labour rebels last week could be doubled in size in votes on education.
"I think there are at least 40 or 50 people who voted with the government on the 90 days detention without charge who would vote against an Education Bill based on the education White Paper," he told ITV1's Jonathan Dimbleby.
Charles Kennedy said Mr Blair was a "wounded animal"
Serial rebel Jeremy Corbyn said Mr Blair would be in "very serious trouble" and could be forced out of office if he went down to another defeat in the Commons.
And former home office minister John Denham urged the government to engage in a two-way dialogue with backbenchers, many of whom were worried about "untested" assumptions to do with policy.
He told BBC Radio 4's Westminster Hour: "What won't work is an approach which just says: `We have decided what we are going to do and we are just going to spend a lot more time explaining it to you'."
But Conservative leader Michael Howard raised the prospect that Mr Blair may be able to rely on Tory support to get flagship policies through Parliament.
"It won't be me making the decisions but my view would be - if what the government brings forward is in the interests of the country we should support them," he said.
Tory leadership hopeful David Cameron also told the BBC's Politics Show he would "resist the temptation" to vote against the government purely to inflict further defeats on Mr Blair.
"I think the temptation to try and bring down the government by voting against something with which you fundamentally agree, I think that is a mistake," he said.
Mr Blair has admitted he faces a "rough ride" but told the News of the World that he and the Cabinet had agreed to "continue doing what is right, not what is easy".
He suggested the government's programme of reforms will target education, hospital waiting times, pensions and welfare benefits.
"All of this will require more difficult decisions and strong leadership....but there is no doubt it will be worth it if, as a result, Britain is better, fairer and stronger," he said.
But Liberal Democrat leader Charles Kennedy described Mr Blair as a "wounded animal" and said his peers would be seeking to overturn his plans for ID cards in the House of Lords on Tuesday.
He told Politics Show: "When you've got a Government which is elected on 36%-37% of the popular vote and it can't carry... its own backbenchers to a sufficient extent, that's a government that needs to think twice about the way in which it goes about public policy."
Earlier, Culture Secretary Tessa Jowell said MPs had a duty to get behind Mr Blair on reforms set out in the Labour manifesto.
She told BBC1's Sunday AM programme: "Every single Labour MP stood on that manifesto and was elected on that manifesto. A manifesto isn't an a la carte menu that you select the bits off that you like."