The Conservatives are accusing Ed Miliband of preparing to "stab the United Kingdom in the back", trading away Britain's nuclear deterrent in order to secure power in a backroom deal with the Scottish Nationalists.
David Cameron has accused the Labour Party of being "in chaos" over its stance on the UK's nuclear deterrent, Trident.
The Prime Minister also said that he supported Michael Fallon's personal attack on Ed Miliband over the issue.
Earlier the Defence Secretary drew on David and Ed Miliband's 2010 leadership contest and claimed that the Labour leader "stabbed his brother in the back" and would do the same to the UK over the renewal of the ageing nuclear programme.
The Prime Minister responds to a reporter who asks if he stands by Mr Fallon's comments on Mr Miliband:
The main political parties are wrangling over whether the UK should spend billions renewing its nuclear deterrent.
If a difference of opinion on defence didn't get in the way of the current coalition - why would it be different for Labour and the SNP?