The government is facing the prospect of resignations and a major backbench rebellion this week over its plans to replace the Trident nuclear weapon system.
The Government's plans have been consistently opposed by churches.
A BBC survey found that of 102 Labour MPs who responded, 61 were planning to vote against the government.
The Telegraph newspaper says that deputy Commons leader Nigel Griffiths has said he cannot back the proposals.
Stephen Pound, an aide to Labour chairman Hazel Blears, and Jim Devine, a parliamentary private secretary to health minister Rosie Winterton, have also indicated that they could leave the government rather than support the proposal.
According to the Financial Times newspaper, ministers will almost certainly have to rely on Conservative support to gain approval for their policy.
Shadow defence secretary Liam Fox said: "When the government is doing the right thing in terms of national security we think they should get the support of the Opposition."
A vote in the House of Commons to be held on Wednesday 14 March 2007 will see MPs urged by Prime Minister Tony Blair and Conservative leader David Cameron to back Trident replacement – in spite of overwhelming opposition from the public and the churches.
The vote will determine whether a new generation of nuclear submarines is to be acquired and the Trident D5 missiles updated. The move will cost some £21 billion over 30 years.
Opponents of the move say that Britain’s nuclear weapons are not properly independent, that they encourage proliferation at a time when international negotiations over Iran’s nuclear capability and North Korea’s ambitions are perilous, and that they make Britain a target for terrorists and others.
It is predicted that the government will win the vote next week, but that there will be a strong rebellion among some – and continuing protests and resistance from peace campaigners.
The churches in Britain and Ireland have been overwhelmingly opposed to Trident replacement, with Catholic bishops and others declaring the threat to use weapons of mass destruction immoral and unacceptable.
The main dissenter has been the Rt Rev Michael Nazir-Ali, Anglican Bishop of Rochester, writing in the Sunday Telegraph newspaper (“I believe in Trident, and using it if necessary”, 4 March 2007).
The Bishop’s opinion piece even appeared to suggest that a pre-emptive nuclear strike against Iran might be justified if it developed nuclear weapons, though, he declared, “the threshold for any such action would have to be very high indeed.”
Last week, Simon Barrow, co-director of the Christian think-tank Ekklesia, said that most Christians would regard him as “profoundly mistaken” in his view that the pre-emptive use of nuclear weapons can be justified on theological grounds.
Commented Barrow: “The bishop’s argument is strategically as well as theologically misplaced. In an age of asymmetric conflict previous notions of ‘deterrence’ do not work as he supposes. Lord Hattersley has correctly observed that you do not dissuade an al-Qaida operative in Baluchistan from attacking Europe by threatening to obliterate Islamabad. You do not discourage Iran from acquiring nuclear weapons by talking about pre-emptive strikes against Tehran, either.”
The Ekklesia director added: “The church’s traditional teaching is that security is to be found in the persuasion of love not the power of death. That is the message 13 US Christian leaders took to Iran a fortnight ago.”