By London reporter Sunita Patel

The election race remained wide open today as the three main party leaders sought to boost their campaigns after a closely-fought contest in the second televised prime ministerial debate.

Polls suggested a dead heat between David Cameron and Nick Clegg, with Gordon Brown trailing despite an improved performance.

Mr Clegg’s bounce in popularity continued despite a concerted attack from Mr Brown and Mr Cameron in the 90-minute showdown. They failed to slow down the Lib Dem leader’s election bandwagon after a week of him riding high in the polls – and a hung parliament is still on the cards.

The leaders adopted a more confrontational approach than last week, clashing on Europe, immigration, nuclear weapons, political sleaze and climate change.

During a first half focusing on international affairs, the leaders returned repeatedly to the dividing lines offered by Europe.

Mr Clegg, hoping to build on his performance in the first debate after weathering the storm of a media attack, flagged up his past experience as an MEP to demonstrate that “we punch above our weight when we stand together in Europe”.

But Mr Cameron attacked the Lib Dem leader for “hypocrisy” and insisted: “I want us to be in Europe, but not run by Europe.”

“These two guys remind me of my two young boys squabbling at bathtime,” the Prime Minister responded, warning that to be “isolated and in the margins” would be a “terrible mistake”.

“David is anti-European, Nick is anti-American, and both are out of touch with reality,” said the PM.

Mr Cameron turned his fire on Mr Clegg by raising the Trident nuclear deterrent, which the Lib Dems oppose renewing, during an exchange on terrorism.

“It’s a real risk to be opposed to a nuclear deterrent,” said the Tory leader, before Mr Brown added: “I say to you Nick – get real. Get real about the danger we face.”

On a hung parliament, the Conservative and Labour leaders, while expressing a readiness to negotiate, emphasised the differences between them. Mr
Clegg said: “When the country is facing very big issues, it is better if politicians actually try and work together.”

Later, Douglas Alexander, Labour’s election co-ordinator, said: “Substance is moving up and style is moving down.” And shadow work and pensions secretary Theresa May hailed a “passionate” performance by Mr Cameron.