Lib Dem leader makes powerful pitch as he depicts his party as a significant change from Labour and the Conservatives

Nick Clegg, the Liberal Democrat leader, stole the first televised leaders' debate in British political history by offering himself up as the fresh and honest alternative to two tired old parties in an electrifying, fast-moving, 90-minute primetime broadcast.

Clegg's revelatory performance, acknowledged by Labour, has the potential to change the political landscape, even if David Cameron, with the most to lose last night, will be relieved that in some of the instant reaction polls he came second, ahead of the prime minister.

Throughout the debate, Gordon Brown was aggressive and tried to launch a pincer movement with Clegg against the Tory leader, but the Liberal Democrat resisted on issues such as democratic reform, inheritance tax and social care.

Clegg, in effect introduced to the nation for the first time, said: "Don't let them tell you that the only choice is between two old parties that have been playing pass the parcel with your government for 65 years now making the same old promises, breaking the same old promises."

The charge reprised his opening claim when he pointed to the other two leaders, saying: "Now, they are going to tell you tonight that the only choice you have is between the two old parties who've been taking it in turns to run things for years."

In the first substantial poll conducted after the debate, Populus for the Times found Clegg the overwhelming winner with 61% and Cameron and Brown trailing on 22% and 17% respectively.

Alan Johnson, the home secretary, said: "Clegg won on style, Brown on substance with Cameron squeezed out."

Though there were no obvious catastrophic errors of judgment by the three men, the foreign secretary, David Miliband, claimed Cameron had insulted a fellow permanent member of the UN security council by at one point in the debate implying that China represented as much of a nuclear threat to the UK as Iran. But overall the quality and the speed of the discussion dispelled fears that the rules would make the 90 minutes stilted or slow-moving.

Brown tried throughout to hit Cameron on the economy and the Tory decision to advocate £6bn of cuts this year. He said: "We've got to make a decision now about how we secure the recovery this year. We've got to make a decision about whether we put funds into the economy or take funds out of the economy. I'm very clear: we mustn't make the mistakes of the 1930s or 1980s when unemployment rose for five years after the official end of the recession. We've got to make sure the money is in the economy this year to make sure that it is secure."

He also repeatedly challenged the Tory leader on his refusal to give guarantees on spending on health schools and hospitals. At one point Brown quipped: "You can airbrush your posters, but you cannot airbrush your policies."

Cameron, standing back from the lectern, secured early impact by apologising on behalf of all the political class for the expenses crisis, and repeatedly tried to use real-life stories to bring home his points to the massive audience.

He also offered a strong peroration. "What you have heard in this debate is just repeated attempts to try and frighten you about a Conservative government. I would say choose hope over fear, because we have incredibly exciting and optimistic plans for the future of our country.

"The great vision where we build a bigger society, when we get our economy moving, when we stop Labour's job tax that could destroy that economy. I think it's been shown tonight that the idea you have to go on wasting money to secure the recovery is simply wrong."

The debate focused on domestic issues, especially crime, immigration, education and cleaning up politics – but rapidly spread right across the political canvas.

The three men played to their perceived political strengths during the debate. At the end of one exchange between Brown and Cameron, Clegg countered in one of the night's more telling hits by saying: "The more they attack each other the more they sound like one another."

Brown relied again and again on his experience.

"These are no ordinary times and this is no ordinary election," he said. "This is the defining year to get these decisions right now. Get the decisions wrong now and we could have a double-dip recession. I know what this job involves and I look forward to putting my plan to you this evening."

Trying to present Cameron as evasive, seen by Labour as one of his weaknesses, he tried to pin the Tory leader down by saying: "This is not Question Time, this is answer time, David."

In one of the more testy exchanges on immigration, Cameron said Britain had benefited from immigration across decades.

"But I do think that it has got out of control and does need to be brought back under control," he said.

The prime minister shot back: "I do not like these words because we are bringing it under control. Net inward immigration is falling and will continue to fall because of the measures we have taken."

Cameron claimed net inward immigration had been around 77,000 under Tory governments but under Labour it had never been below 140,000.

Clegg said: "What has gone so wrong is talking tough and delivering chaos in the way that it is run."

The Conservative leader tried to put distance between the Tories and 13 years of Labour – and attempted to draw the sting out of the toxic issue of MPs' expenses.

He said: "Your politicians – frankly, all of us – let you down. We can go on as we are, or we can say: 'No, Britain can do much better.' We can deal with our debts, we can get our economy growing and avoid this jobs tax, and we can build a bigger society."

Cameron admitted that not everything Labour had done over the past 13 years had been wrong, and he would keep the good things.

"But we need change, and it's that change that I want to help to lead."

• This article was amended on 16 April 2010. The original reported David Cameron as saying net inward immigration had been around 7,000 under Conservative governments. A post-debate opinion poll conducted for the Times was said to be by YouGov. This has been corrected.