Foreign Secretary Michael Fallon has "demeaned himself and demeaned his office" by launching a scathing attack against Labour, according to Ed Miliband.
The Labour leader hit back after the senior Tory claimed Miliband would "stab the UK in the back" if he entered Number 10 after the general election by scrapping the UK's nuclear defence system, Trident, in a bid to form a partnership in Westminster with the SNP.
"Fallon is a decent man but today I think he has demeaned himself and demeaned his office," Miliband argued.
"National security is too important to play politics with. I will never compromise our national security, I will never negotiate away our national security.
"And you know what, the Conservative party can throw what they like at me, but I'm going to concentrate on the issues that matter to the British people - how we keep our country safe, how we invest in education, how we tackle tax avoidance, how we make this country work for working people.
"I've got to say, I think the British people deserve better than what the Conservative party are offering in this campaign, which is a campaign based on deceit and lies."
Fallon launched the personal attack ahead of promising that the Tories would build four Successor Ballistic Missile Submarines as part Britain's Trident programme.
"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," he wrote in The Times.
Labour have maintained they are committed to renewing Trident but the party are looking into options to reduce the number of submarines to three.
However, the SNP have rejected plans to renew the defence system and Nicola Sturgeon has described the issue as a "red line" the party would not cross.
The nationalists are set to take a swathe of seats from Scottish Labour on 7 May, with a recent poll from YouGov putting the party 19 points in front (46% vs 27%).