Nick Clegg's bandwagon appeared to have kept up its momentum last night at the end of a second far more personalised leaders' TV debate in which he made an emotional final appeal: "Don't let anyone tell you that this time it can't be different – it can."

Expecting a backlash from Gordon Brown and David Cameron following a week in his which his popularity has surged, Clegg appeared to hold his own, and a slew of instant polls showed continuing and robust support for his party – a Guardian/ICM poll last night gave Clegg victory.

But all the party leaders appeared to have upped their game from last week.

Gordon Brown, giving a far more prime-ministerial performance, opened by admitting: "If it is all about style and PR, count me out." But he made some pointed attacks and rounded on Clegg in particular over the Liberal Democrats' stance on nuclear disarmament, telling him to "get real".

David Cameron was noticeably more relaxed, although he failed to deliver the key knockout blow against Clegg that he needs at some point if he is to secure an overall majority at the election. The Tory leader repeatedly argued that his was the only party that could deliver change.

"It's clear from last week's debate that the country wants change but the question is: what sort of change and who is best placed to lead that change? If you vote Conservative you will get a new team and you won't be stuck with what you've got now," he said.

At the only point in the debate in which he appeared to get angry, he accused Brown of sanctioning leaflets full of lies over Tory plans to cut pensioners' benefits.

Last night's outcome suggests that the dynamics of the campaign – which saw the Lib Dems emerge as a powerful third force in the election – have not been reversed.

An hour after the end of the debate, a Guardian/ICM poll of 504 voters who watched the broadcast gave Clegg a narrow win, with the Lib Dem leader on 33% and Cameron and Brown on 29% each.

Brown, however, was considered the best potential prime minister of the three: he was on 35%, with Cameron on 33% and Clegg on 26%.

Other instant polls suggested different winners, with Cameron topping one clearly, and Clegg winning in two. Taken overall, the polls amounted to almost a dead heat, but Brown failed to top any of them despite a markedly improved performance. He will hope he can improve again in the final debate on BBC1 next week, which will focus on the economy.

After the stunning surprise impact of his first TV debate, Clegg was unlikely to have the same revelatory impact a second time. Nevertheless, he appeared to negotiate the potentially dangerous waters of his policies on Europe, immigration and the independent nuclear deterrent.

In one of the more memorable moments of the night, Brown rounded on the Liberal Democrat leader, telling him to "get real" on the need to replace Trident, and accused him of favouring an amnesty for illegal immigrants.

On Trident, Brown turned to Clegg and said: "I have to deal with these situations every day and I say to you Nick: get real. Get real. Because Iran, you're saying, might be able to have a nuclear weapon and you wouldn't take action against them but you're saying that we've got to give up our Trident submarine and our nuclear weapons now. Now get real about the danger that we face if we have North Korea, Iran and other countries with nuclear weapons and we give up our own."

Cameron also rounded on Clegg on this issue, saying he agreed with Brown. "You cannot put off these decisions. You have to make them early – you cannot rustle up nuclear deterrent at the last minute."

After a week in which senior Tories have warned that a hung parliament would be a disaster for the country, Cameron appeared to backtrack, saying: "If there is a hung parliament, we will have to be responsible and do our best to make it work."

Clegg appeared to seize on this. "If a hung parliament happened the world won't end, and it will be your choice," he told the voters, adding: "And if the people think no one party deserves support, then the parties have to accept that and work together. We don't simply need to choose from the old choices of the past, we don't need to repeat the mistakes of the past."

With much riding on his second performance, he betrayed the huge stakes, saying in his closing statement that the country was on the verge of "one of the most exciting elections we have had in a very long time. People are beginning to hope we can do something different this time. Don't let anyone tell you this time it can't be different: it can."

Earlier, Clegg tried to project himself as a modern, reasoned patriot, saying he was proud of the values that had made our country great – "human rights, democracy, the rule of law". But he went on: "The sad truth is that in recent years our governments, under the two old parties, have let those values down. We shouldn't have sent our troops into harm's way without the right equipment and decent pay. We shouldn't be facing allegations that we were complicit in torture. We shouldn't have invaded Iraq."

Brown continued to be the most combative of the three men, but also addressed his own weaknesses with candour – making a startling admission about his own unpopularity and inability to communicate.

"This may have the feel of a TV popularity contest. But in truth, this election is a fight for Britain's future. Your future and your jobs. If it's all about style and PR, count me out. But if you want someone to make decisions, and with the judgment and a plan for the future, I'm your man.

"Like me or not, I have a plan for Britain's future. And the way to do it is with a majority Labour government."