Cameron demands withdrawal of Labour leaflets in 'lies' row

Mr Cameron said the Prime Minister should be "ashamed" of the leaflets, which he said lied about his party intending to halt benefits for pensioners such as a winter fuel allowance.

The row ignited what had been relatively calm debate and was followed by more angry exchanges on immigration, with Mr Cameron and Mr Brown turning on Nick Clegg over what they claimed was his policy to offer an "amnesty for immigrants".

The format, which was the same as the first ever televised election clash between British political leaders last week, with each being given a chance to answer questions from the floor before an open debate.

The theme was international affairs followed by domestic issues of the economy and electoral reform.

But having launched the General Election battle with pledges by all parties to run positive campaigns, the debate descended into a bitter exchange over Labour's election leaflets.

Mr Cameron accused Labour of "disgraceful" smears over Tory plans on benefits for pensioners, saying leaflets going out across the country were spreading lies.

He pledged to keep the winter fuel allowance, free TV licenses and free bus passes for pensioners, but Mr Brown questioned why the Tory manifesto did not pledge to keep free eye tests for the elderly as well.

Mr Cameron snapped back: "We'll keep them. Will you now withdraw your leaflets saying the Conservatives would take away things like free bus passes? You really should be ashamed of doing things like that."

But Mr Brown said he had never "authorised" any such leaflets, and questioned Mr Clegg's proposals to reform the winter fuel allowance.

Angry clashes continued on the subject of immigration, with Mr Brown and Mr Cameron describing the Liberal Democrat proposal to allow illegal migrants to earn the right to stay in the UK after a fixed period as an "amnesty" which would attract more people to come to Britain.

Mr Cameron said: "The country wants and deserves firm immigration control. We need to get back to the days when immigration was not a political issue.

"It is out of control – that is Labour's fault – and what the Liberal Democrats are proposing would make things much worse."

Mr Clegg admitted his plans were "controversial" but said there needed to be an "honest discussion" on the issue.

Firing back at his opponents, he said: "You cannot deport 900,000 people if you do not know where they live."

He added: "We are saying let's get them to leave the shadows and get them to play by the rules, speak English and pay into the tax system."

Alliances in the debate surprisingly swung between the leaders as they took it in turns to unite or attack one another.

It had been expected that Mr Cameron and Mr Brown would join to try and bring down Mr Clegg with the pair trailing the Liberal Democrat leader in the polls but there appeared to be few tactics in the arguments.

Mr Clegg came under attack from the two other leaders over his policy not to commit to renewing the Trident nuclear deterrent because of the vast cost of the project.

Gordon Brown told him to "get real" and in a rare moment of unity, David Cameron declared: "I agree with Gordon".

Mr Cameron faced a two pronged attack on his European policies as Mr Clegg and Mr Brown ganged up in an attempt to reopen old wounds in the Tory party.

The Tory leader was accused of siding with "nutters and anti-Semites" in the European Parliament, after his decision to form a new group including Poland's homophobic Law and Justice party.

But he retorted: "I want to be in Europe but not run by Europe.

"People are angry that politicians in Westminster have given away powers without asking them first."