Tories 'in the gutter' - Miliband
Ed Miliband has angrily accused the Conservatives of dragging the election campaign "into the gutter" after they claimed that he would "stab the United Kingdom in the back" over the renewal of the Trident nuclear deterrent.
The Labour leader called on David Cameron to "get a grip" on the Tory campaign after Defence Secretary Michael Fallon warned that Labour's refusal to rule out a deal with the Scottish Nationalists was putting the future of the deterrent at risk.
But the Prime Minister strongly backed his Cabinet colleague, accusing Labour of "playing fast and loose" with the country's security by leaving open the door to an agreement with the SNP who are committed to scrapping Trident.
The bitterest and most personal exchanges of the campaign so far were prompted by an incendiary intervention by Mr Fallon suggesting the way that Mr Miliband challenged his elder brother, David, for the Labour leadership showed the lengths he would go to to gain power.
Writing in The Times, he said: "Ed Miliband stabbed his own brother in the back to become Labour leader. Now he is willing to stab the United Kingdom in the back to become prime minister."
Furious Mr Miliband responded by accusing the Conservatives of running a campaign based on "deceit and lies".
He insisted that Labour was fully committed to renewing the Trident submarine missile fleet and said the Defence Secretary's comments showed the Conservative campaign had "descended into the gutter".
"Michael Fallon is a decent man but today I think he has demeaned himself and demeaned his office," he said during a campaign event in London.
"National security is too important to play politics with. I will never compromise our national security, I will never negotiate away our national security.
"David Cameron should be ashamed. He's got nothing positive to say about the future of the country, he's got no forward vision for the country. And he sends out his minions, like Michael Fallon, to engage in desperate smears.
"I think decent Conservatives right across our country, decent Conservative MPs, decent Conservative Party members, decent people right across Britain, will say 'Come on, we're better than this kind of politics'."
Mr Cameron, campaigning in the East Midlands, insisted that Mr Fallon had been right to raise the issue, and challenged Mr Miliband to rule out any arrangement with the SNP that would put Labour into power after the election on May 7.
"It is important that in a dangerous, insecure world we have that ultimate insurance policy," he said of Trident. "When I listen to what Labour are saying, they are playing fast and loose with the country's security."
In a speech in London, Mr Fallon confirmed that a Conservative government would go ahead with the construction of four new Trident nuclear missile submarines to replace the existing fleet of ageing Vanguard-class boats.
He warned that it would be put at risk by the prospect of Mr Miliband "limping into office aided by the crutch of the SNP", whose leader Nicola Sturgeon has made clear that the price of their support would be the abandonment of Trident.
"When Britain could face nuclear blackmail by rogue states, this self-indulgent approach is more suited to a student protest group than a party of government," he said.
"It is a sign of Ed Miliband's weakness that he has failed to rule out a deal. In the absence of that assurance, voters can only conclude that he would be prepared to barter the future of Britain's national security for power."
Ms Sturgeon confirmed that any agreement by her party to support Labour in a hung parliament through a "confidence and supply" arrangement would have to rule out Trident renewal.
"Both Ed Miliband and I have said that a coalition is unlikely, any confidence and supply arrangement would involve the non-renewal of Trident," she told Sky News.
"If we are not in any kind of formal arrangement with Labour and voting on an issue-by-issue basis, we will not vote for anything that facilitates the renewal of Trident - I can't be any clearer than that."
Liberal Democrat leader Nick Clegg said it was "quite extraordinary" that the Conservatives had chosen to elevate "this nuclear weapons system" to the most important issue of the campaign.
"I think many people would find it pretty odd that a major party like the Conservative Party think that's more important than delivering jobs or fairer taxes or better pensions or money for our schools and nurseries and colleges," he told LBC radio.
Nigel Farage waded into the row, saying he feared the election campaign was turning into "an American, negative, shouting match".
Speaking on a visit to Broadstairs in Kent, the Ukip leader said: "The attack on Ed Miliband was very, very personal, calling him a backstabber.
"I just fear that we have an election campaign that is turning into an American, negative, shouting match between two parties, and I don't think the public like it.
"I certainly don't."
During a visit to Norwich, Green Party leader Natalie Bennett said: "A very important issue has been raised in the debate about Trident today but the way in which it was raised is deeply damaging.
"This kind of personalised attack is the kind of Punch and Judy politics that is really damaging our political fabric. "
Education Secretary Nicky Morgan was unapologetic about the highly-personal attack.
"I'm afraid to say that when you ask people about Ed Miliband, the thing that most people know about him is the way that he did stab his brother in the back.
"That goes to the judgment people make about him letting the country down," she told LBC radio during a debate between leading female politicians.
"We can have a debate about exactly where the knife entered."
Labour deputy leader Harriet Harman said the "concerted, malicious" tactic "really brings our politics down" and said it was the same as a controversial newspaper article attacking Mr Miliband's late father.
"At least Cameron sounded a bit shame-faced about it today," she said.
Ms Morgan hit back: "I can tell you that people on the streets of where I am campaigning are saying a lot worse things about your leader, Harriet, and the kind of leader he would be. It is absolutely right to point it out."