The Government may replace Britain's Trident nuclear weapons system without offering MPs a vote on the project.
Downing Street said there would be a "proper debate" on whether to renew the independent nuclear deterrent but stopped short of granting demands by 93 Labour MPs for a full-scale parliamentary vote on the scheme.
Gordon Brown, who announced his personal support for replacing Trident on Wednesday, wants to restore trust in politics by boosting Parliament's powers - for example, by guaranteeing MPs a vote before the nation goes to war.
The Chancellor believes MPs could be persuaded to support a new nuclear weapons system but accepts that a final decision will have to be taken by the Cabinet, with Tony Blair and the Commons Leader, Jack Straw, in the lead. Some ministers fear that allowing a vote would turn into a procedural nightmare with attempts by opponents to wreck the project. They might also need to rely on the support of Tory MPs to win the vote.
Mr Straw echoed No 10's line by declining to promise a vote. He told the Commons there would be a White Paper on Trident followed by a parliamentary debate "in a form which shows proper respect for this House".
Peter Hain, the Northern Ireland Secretary and a likely candidate for deputy Labour leader when John Prescott stands down, backed the Chancellor. He said: "As Gordon Brown has said it is absolutely right that we make the right long-term decisions for our national security, including retaining our independent nuclear deterrent. It is important that the detail of how we implement this manifesto commitment should be the subject of full debate in the party and in Parliament."
Whatever the decision on a vote, Labour MPs fear they will be presented with a fait accompli by the time they discuss the issue. The Commons debate is expected early next year - after the Cabinet makes a decision in principle. Ministers insisted they had to "give a lead", with the different options ranging from £10bn to £25bn.
Mr Brown's surprise move provoked a furious reaction from Labour opponents of updating Britain's nuclear deterrent. His friends were relaxed about that, hoping that it would reassure voters that he would not position himself to the left of Mr Blair if, as expected, he succeeds him as Prime Minister.
Critics said that the Chancellor's intervention could reduce his level of support in the Labour leadership contest, although he is still likely to crush a left-wing rival running on an anti-Trident ticket.
Clare Short, a former cabinet minister, said: "It means a lot of people who were happy to see Brown take over as leader will now think there's got to be a contest and we're not willing to support him. I won't support him. I mean this is outrageous, unless he changes his mind."
John McDonnell, who chairs the left-wing Campaign Group of MPs, said: "The whole tenor of the Chancellor's speech is a slap in the face for the Labour and trade union movement. Gordon has laid down a clear marker for the approach he intends to take to the leadership of the party. It is a worrying sign that he is prepared to ignore the strong feelings of Labour Party members and trade unionists on this and other key issues of concern."