Tony Blair is facing a political backlash over his decision to order a new generation of nuclear weapons to replace the ageing Trident fleet at a cost of billions of pounds.
Rebel Labour MPs will meet tomorrow to coordinate their fight against his plans, which seem set to provoke one of the biggest shows of opposition to Mr Blair from inside his own party since the start of the Iraq war.
Opposition to an updated version of Trident goes far beyond MPs who object to nuclear weapons on principle.
It includes senior figures in the military, who question whether this is the best way to spend a tight military budget.
A senior defence department source told the Independent that there was "a serious debate" going on "at all levels" over the long-term role of the armed forces and whether a nuclear deterrent was still needed.
The Chancellor, Gordon Brown, is believed to have privately queried the huge cost.
An indication of the sums involved was revealed last week when the Defence Secretary, John Reid, released updated figures showing that Britain's nuclear bomb factory at Aldermaston has been given a £2bn budget for the next three years.
The cost of running the Atomic Weapons Establishment has averaged £300m a year, at current prices, since 2000.
Next year's costs will jump to £507m, rising still higher to about £1.5bn over the next two years.
Officially, the task of Aldermaston's scientists is to ensure that the Trident fleet is kept in working order.
Their real task, according to military sources, is to make sure that the scientific know-how is in place to create a whole new generation of nuclear weapons as soon as a political decision has been made.
The Independent revealed in May that Mr Blair had decided to go ahead with a replacement for Trident, at a total cost likely to exceed £10bn, but that he was delaying the announcement until after the general election.
In June, the Prime Minister announced that he wanted to "listen" to the views of MPs before making afinal decision.
However, both he and Mr Reid have pointedly avoiding saying that MPs will be given an opportunity to vote on the nuclear issue.
The "listening exercise" promised by Mr Blair began at the end of last week when Mr Reid's parliamentary private secretary, Siobhain McDonagh, sent an email to all Labour MPs inviting anyone concerned about nuclear weapons to meet the Defence Secretary in groups of six at a time.
Although Trident's life could be extended for another 20 years, a decision on whether to replace it has to be made much sooner, because of the long"lead-in" time needed to develop and test new weapons.
Mr Blair is thought to be determined to have the matter settled before he leaves 10 Downing Street.
He believes that Britain owes it to the US to remain a member of the nuclear club.
Yesterday, Mr Blair and the Foreign Secretary, Jack Straw, held talks at Chequers with the US Secretary of State, Condoleezza Rice, about the worsening relations with Iran.
The US government, backed by Britain, is intent on preventing Iran from developing nuclear weapons.
Critics say Britain's case is weakened if Mr Blair insists on rebuilding Britain's nuclear arsenal.
Three Labour MPs - Gordon Prentice, Paul Flynn and John Austin - have drawn up a resolution questioning the cost of Trident, and have demanded a vote on it at one of the meetings whichLabour MPs hold every Monday.
Mr Flynn, a member of the Defence Committee of the Western European Union, said: "We haven't got any enemies that we could possibly want to aim nuclear weapons at now.
The case that John Reid has given for these weapons is that we might possibly have the right sort of enemy in 15 years time, which doesn't seem like a good reason for spending billions of pounds.
Our future role is going to be as peacekeepers, in which we perform better than anyone else.'"Last week, Mr Prentice met the chairman of the parliamentary party, Ann Clwyd, who urged him to drop the idea of forcing a vote, fearing that it would give an impression of a divided Labour Party.
She also warned them that they would probably be defeated, and that even if they won, they would not alter government policy.
"We said we were prepared to be reasonable.
If she didn't want a vote in the parliamentary Labour Party, then John Reid should come to come to the Commons so that we could have a vote there," Mr Prentice said.
If they are not promised a Commons vote, the rebels have marked 31 October as they day they will force a vote among MPs.
Peter Kilfoyle, a former defence minister, said: "This is at a time when they are going to cut down on both the navy and the air force.
It requires a whole review of the nuclear stock and what it is for, when even the Americans are developing different types of nuclear weapons.
"But there is also the politics and the macho posturing, and the issue of jobs, which we will hear a lot about."Asked about the reason for the doubling of Aldermaston's budget, a Ministry of Defence spokesman said: "The planned expenditure is aimed at maintaining key capabilities at the Atomic Weapons Establishment to ensure that we can safely support the Trident warhead throughout its planned in-service life.
"In the absence of the ability to undertake live nuclear testing, given that the UK has signed and ratified the Comprehensive Test Ban Treaty, it is necessary to invest in the facilities at AWE which will provide continuing assurance that the existing Trident warhead stockpile is reliable and safe."