The future of Britain's independent nuclear deterrent sparked a bitter war of words yesterday. Tories claimed Russian leader Vladimir Putin would be happy with Ed Miliband as prime minister because he cannot be trusted to keep our Trident submarines. Defence Secretary Michael Fallon led a ferocious assault on the Labour leader – claiming he is a 'backstabber' who cannot be trusted not to sell out in a 'grubby' deal with the SNP. Scroll down for video . Tories also pointed to a survey suggesting up to three-quarters of Labour election candidates oppose the replacement of Trident. Business and skills minister Nick Boles, a close ally of David Cameron, went further, claiming the Russian president would be pleased to see Mr Miliband enter Downing Street propped up by SNP leader Nicola Sturgeon. 'Ask yourself this. Who does Vladimir Putin want to see running Britain after May 7?' Mr Boles demanded. 'Answer: the man who abandoned the Syrians to their fate and the woman who wants to scrap our nuclear deterrent. He… stood alongside Putin in protecting [Syrian President] Assad.' Mr Miliband reacted with fury to the attacks, accusing the Tories of 'desperate smears' and dragging the election campaign 'into the gutter' by claiming he would 'stab the UK in the back' in the same way that he did brother David in the Labour leadership contest. 'David Cameron should be ashamed,' Mr Miliband said, insisting that Labour was committed to renewing the Trident fleet. But Mr Fallon's promise to renew all four submarines appeared to leave Labour in disarray. Mr Fallon said the full replacement of Trident would be a 'red line' in any second Conservative-Liberal Democrat coalition. 'I want to see multilateral disarmament, I'm not in favour of unilateral disarmament. That means we have got to have the least cost deterrent that we can have.' - Ed Miliband, January 5 . 'We're going to see whether there's any way you could do it with three [submarines].' - Ed Balls, March 15 . '[Four submarines] is exactly the policy that we have had for a very long time.' - Chris Leslie, Wednesday . 'Four boats... but we'll look at that in government.' - Douglas Alexander, yesterday . 'It's right to have a review because technology changes.' - Ed Miliband, yesterday . For Labour, however, frontbenchers gave differing positions. Some suggested a Labour government might cut the number of submarines. Mr Miliband said he favoured 'basically four boats' but it was 'right to have a review' while Labour treasury spokesman Chris Leslie said that maintaining four submarines was 'exactly the policy that we have had for a very long time'. Earlier this year Mr Miliband had said he favoured the 'least cost deterrent' possible. And in March, Shadow Chancellor Ed Balls had said the party would see whether three submarines could suffice. Military experts insist four submarines are the minimum needed to ensure Trident can be deployed at sea at all times. Any fewer would mean that the missiles would on occasion be left vulnerable in port. Mr Fallon attacked the idea of having only three, saying there was no point in having a deterrent that 'takes the weekend off'. A survey of Labour candidates, conducted by the Campaign for Nuclear Disarmament, suggests that Mr Miliband would have difficulty carrying large sections of his party with him if he sought to renew Trident. In several Labour safe seats, MPs who supported Trident are being replaced by candidates who oppose it. They include Meg Munn in Sheffield Heeley, whose replacement Louise Haigh says: 'Investment in nuclear is immoral in and of itself'. Former Defence Secretary Liam Fox said the lack of clarity from Labour over Trident left Britain in a 'very dangerous position'. 'Unless we are absolutely sure where they would be then we have to assume that they are not fit to protect this country by having a continuous nuclear deterrent,' he said 'In a very dangerous world that is a very dangerous position.' As many as three-quarters of Labour candidates oppose the replacement of Britain's Trident nuclear deterrent. Pictured is the HMS Victorious off the coast of Scotland . CND's survey of Labour candidates suggested as many as three-quarters opposed the replacement of Britain's Trident nuclear deterrent. The anti-nuclear group said last month it had polled a 'representative sample' of Labour candidates, including sitting MPs. But Labour critics claimed only 73 candidates had been surveyed with 50 or so anti-Trident. The finding suggested anti-nuclear Labour MPs could make common cause with the Scottish National Party, which has said it wants to ditch Trident. Labour's official policy is to maintain a continuous, submarine-based deterrent. But many senior figures want Labour to back a more limited, cut-price deterrent – while others believe the party should scrap it altogether. Kate Hudson, CND's general-secretary, said: 'Labour candidates are in step with public opinion. The majority of the public don't want tosee £100 billion spent on nuclear weapons.' Mr Cameron backed Mr Fallon's attack and challenged Mr Miliband to rule out any arrangement with the SNP that would put Labour into power. He said: 'When I listen to what Labour are saying, they are playing fast and loose with the country's security.' Miss Sturgeon said: 'We would never be in any deal with a Labour government who is going to renew Trident.'
Tories say Russia's Vladimir Putin would be happy with Ed Miliband as PM . This is because he cannot be trusted to keep Britain's Trident submarines . Defence Secretary Michael Fallon said Labour could sell out in a SNP deal . Mr Miliband reacted with fury, stating David Cameron should be 'ashamed'