Ex-Defence Secretary Bob Ainsworth has said Labour may re-consider its support for replacing Trident.
In a debate in the Commons, he said the decision that the Ministry of Defence must fund the replacement for Trident meant that in real terms the MOD faced a cut of 13% rather than 8%.
He said delaying the decision to go ahead would increase the overall cost.
"My own party may well as a result of that... have to look at whether we maintain our position on Trident."
He said that if there was to be no decision for five years and if the cost would fall solely on the defence budget at the cost of other military capability "then we are going to have to think seriously about whether or not there is another way... of maintaining Britain's deterrent, without the huge cost cutting expenditure on the rest of our armed forces."
When he was challenged by the Defence Secretary Liam Fox on his apparent change of position, Mr Ainsworth said that if Labour did not examine its stance on Trident it would be seen as putting its head in the sand.
Mr Ainsworth's comments comes just over a month after he rejected calls from his former ministerial aide Eric Joyce for a rethink of Labour's policy on Trident.
The pair clashed at a fringe meeting at Labour's annual conference, with Mr Joyce accusing his former boss of being to the right of the Conservatives on the issue and of "personally" blocking a full review of Labour's foreign and defence policy, including Trident, when Labour was in power.
Mr Ainsworth firmly rejected the claim and said he had done his best to generate debate among Labour MPs about the future of Britain's nuclear deterrent when Labour passed legislation committing the UK to replacing Trident, when Mr Ainsworth was a government whip.
He had earlier accused the Liberal Democrats of "immaturity" and threatening the national interest, after Lib Dem defence minister Nick Harvey said delaying the final decision on replacing Trident until after the next general election would turn it into a political "hot potato" for Labour.
Former Prime Minister Gordon Brown was at pains to stress Labour's commitment to Trident ahead of the general election, but his successor as Labour leader, Ed Miliband, has indicated that although he remains committed to maintaining a constant nuclear deterrent, he would be prepared to review a "like-for-like" replacement of Trident.
In a separate development, The Treasury has published the letter from BAE Systems chief executive, Ian King, to the prime minister explaining that it would cost the government more to cancel two new aircraft carriers than to build them.
Chancellor George Osborne reluctantly agreed to fund the two carriers, even though the UK will not have planes to fly on them for at least 10 years following the cancellation of the Harrier jump jet and one of the ships will be immediately mothballed.
The letter says the deal to build the ships "was underpinned by an agreement with MOD that in return for a guaranteed level of funded work, we (BAE) would sustain in the UK the key capabilities needed for warship design, development, build, integration and support and would rationalise and transform the business."
It says "If both carriers are completed the cost will be £5.2bn. If Prince of Wales is cancelled, the direct cost of the programme will be £4.8bn. However in these circumstances, and under Treasury rules and the agreements I have outlined, there will be consequential costs, including those related to rationalisation, which we estimate would amount to £690m. "
The letter goes on: "the cancellation of Prince of Wales would mean that production in all BAE systems shipyards would cease at the end of 2012.
"There is no further production work planned until steel is due to be cut on the new frigate programme in 2016.
"This means that the business would be unsustainable, and all three yards would have to close by early 2013, with the loss of more than 5,000 jobs in BAE systems and many more across the UK in hundreds of companies in the supply chain.
"In practice that means the end of the UK's capability in complex warships and would bring the sector to a halt."