Nick Clegg pleaded for Liberal Democrat activists to "stick with" him today after he suffered a major rebellion over key coalition school reforms.
Delivering his first party conference speech as Deputy Prime Minister, Mr Clegg mounted an impassioned defence of his decision to do a deal with David Cameron's Tories.
He said voters would never have taken the Lib Dems seriously again if they had passed up the opportunity to govern in the national interest at a time of crisis.
And he insisted the "soul" of the party was alive and well in the coalition despite members' fears that they were being marginalised and suffering serious political damage.
The address - a text of which was shown to the Prime Minister before being finalised - came after a difficult day for the leadership.
Just hours before Mr Clegg took to the stage in Liverpool, party members overwhelmingly backed a boycott of Tory-inspired plans for a network of "free" schools.
Attempts by the leadership to water down the criticism by removing claims that the policy would increase "social divisiveness and inequity" were resoundingly thrown out following a passionate debate in the packed hall.
Mr Clegg told the audience at the Arena and Convention Centre that he knew many of the coalition's plans would "provoke controversy" and some Lib Dems were "worried" about the schools plans.
"It wouldn't be Liberal Democrat conference if we didn't have a motion that provoked strong passions on both sides," he said.
"The great thing is that all Liberal Democrats share a passion for education. When it comes to lasting fairness, education is everything.
"So I want to be really clear about what the Government is proposing. It's not Labour's academies programme: a few schools singled out for preferential treatment - a cuckoo in the nest that eats up attention and resources."
He went on: "My vision is that every school, in time, will be equal, every school equally free. But there's one freedom new schools shouldn't have: freedom to select."
Mr Clegg reiterated his reasons for forging the Tory alliance, saying the "chance for change" came, and the Lib Dems "responded with real courage and conviction". He praised the Conservatives for being willing to "embrace negotiation and compromise".
"Cynics expected us to back away. Instead, we confounded those who said that coalition Government was impossible. We created a Government which will govern, and govern well, for the next five years," the Deputy Prime Minister said.
"Hold our nerve and we will have changed British politics for good. Hold our nerve and we will have changed Britain for good."
The coalition was the "politics our nation needs today", he said.
"In life, two heads are usually better than one. And in politics, too, when the country faces grave challenges - the deficit, the threat of climate change, a war in Afghanistan, millions of children trapped in disadvantage - two parties acting together can be braver, fairer and bolder than one party acting alone."
Mr Clegg told Lib Dem members that their long-standing desire for fundamental reform of the UK's electoral system was now within reach - and also had an apparent dig at Mr Cameron for repeatedly warning before the general election that a hung parliament would be disastrous.
"Never again will anyone be able to frighten the voters by claiming that coalition Government doesn't work," the party leader said.
"Liberal, plural politics will feel natural; the sane response to a complex and fast-changing world. Just imagine how different our country will be."
He highlighted a list of long-term Lib Dem goals that the coalition was already implementing, saying it had "ended the injustice of the richest paying less tax on investments" and "guaranteed older people a decent increase in their pension".
Legislation that was "illiberal and intrusive" was being rolled back, a bank levy introduced, and 900,000 low earners are being taken out of income tax altogether.
"In May, the people of Britain will get to choose their own voting system," Mr Clegg said. "And this time next year, there will be a pupil premium so the children who need the most help get the most help."
He went on: "We've always been the face of change. We are now the agents of change. And every single person in this room is part of that change."
In a crowd-pleasing reference to the Lib Dems' long-term opposition to the Iraq War, Mr Clegg defiantly repeated his opinion that the invasion had been illegal - despite previous warnings that such comments could open the Government to legal action.
Insisting his new-found status had not changed his views, the Deputy Prime Minister said: "I still think the war in Iraq was illegal. The difference is, lawyers now get anxious when I mention it."
He added: "We will never lose our soul. We haven't changed our liberal values. Our status is different but our ambition is the same."
Turning his fire on Labour, Mr Clegg accused it of "squandering a golden age" of 13 years when it had large majorities and benign economic conditions, and left the country "on the verge of bankruptcy".
He said that as a result, the coalition's biggest task is to tackle the deficit - but he insisted that planned cuts do not amount to an "ideological attack on the size of the state".
"There is one reason and one reason only for these cuts. As Liam Byrne said in that infamous letter: there isn't any money left," he said.
Despite thousands of jobs being lost already, the Lib Dem leader suggested that the pain of the crisis was "invisible" and had not been felt yet.
"You can't see the debts mounting up," he said. "Walk the high street, go to work, talk to your friends, you won't see the signs of our debts or our deficit. The numbers sound alarming, but in the end they're just numbers. It doesn't feel like we can't afford things."
Appealing for Lib Dem activists to keep the faith with the new Government, he held out the "prize" that by the next general election in 2015 Britain would be a "different country".
"The years ahead will not be easy but they will make the difference our country needs," Mr Clegg said.
"Stick with us while we rebuild the economy. Stick with us while we restore our civil liberties, protect our environment, nurture our children and repair our broken politics.
"Stick with us and together we will change Britain for good."
Mr Clegg insisted the Comprehensive Spending Review (CSR) was not about "slash and burn", and said cuts would be conducted "fairly" rather than repeating the "mistakes of the 1980s".
But he defended the choice to make reductions at a faster pace than Labour had proposed.
"We could have decided to go more slowly but it would have worsened, not eased, the pain," he said. "Because every day you ignore a deficit, it gets harder to fix. The debts mount up and you have to pay interest on them.
"Already we are spending £44 billion a year on interest alone.
"Under Labour's plans, that would have risen to nearly £70 billion. A criminal waste of money that shouldn't be lining the pockets of bond traders. It should be paying for police, care workers, hospitals and schools."
The Lib Dem leader conceded that curbs on welfare, which could include universal benefits such as child benefit, would be "controversial".
But he did not make any reference to the issue of Britain's nuclear deterrent. Mr Cameron has committed the Government to the like-for-like replacement of Trident, despite strong objections from the Lib Dems.
The 37-minute speech was greeted with the regulation standing ovation, which lasted until Mr Clegg left the hall accompanied by wife Miriam.