Cameron 'committed to nuclear deterrent'

But the Prime Minster said it was right to explore how to get the best "value for money" when replacing the ageing Trident system.

The comments came as the row over the cost and shape of the UK's nuclear capability intensified.

Senior Tories expressed alarm at reports that the Government could put off the final decision on whether to go ahead with the replacement of the four missile-carrying submarines – due to be announced in 2014 – until after the election in 2015.

The head of the UK armed forces, Air Chief Marshal Sir Jock Stirrup, also waded into the controversy by warning that the Government may as well scrap the deterrent altogether if weapons were only deployable intermittently.

However, asked directly yesterday whether he was committed to keeping a continuous-at-sea deterrent, Mr Cameron replied: "Yes, of course."

He added: "We believe in Britain's independent nuclear deterrent. We believe in maintaining it, we believe in updating it and the coalition agreement is very clear about that.

"But at the same time it is quite right we should ask the question 'Are we getting full value for money from the renewal that will take place?'

"It is right that we should ask those questions and that's exactly what's taking place now."

Moving to delay the replacement of Trident could ease both the pressure on the over-stretched defence budget and political tensions within the coalition, with the Liberal Democrats pressing for a cheaper alternative.

But Conservative MP Bernard Jenkin, a former defence spokesman, warned that any postponement would be unacceptable to Tories.