A group of MPs has failed to force a vote among Labour backbenchers on the future of Britain's nuclear deterrent.
A decision on a Trident replacement is due this parliament
Labour MP Gordon Prentice put down a motion for the Parliamentary Labour Party to debate the wisdom of spending an estimated £20bn to replace Trident.
But he said the motion had "disappeared into the ether".
Defence Secretary John Reid said no decision on replacing Trident had been taken. But he said Labour was committed to keeping Britain's nuclear deterrent.
The issue of nuclear weapons is divisive within the Labour Party, which at one time supported the policy of unilateral disarmament.
Last week, a group of writers, led by Nobel Prize winner Harold Pinter, wrote an open letter to MPs in The Guardian saying there was "no legitimate political, military or moral reason" for replacing Trident.
Length: 44ft (13m)
Weight: 130,000lb (58,500kg)
Diameter: 74 inches (1.9m)
Range: More than 4,600 miles (7,400km)
Power plant: Three stage solid propellant rocket
Cost: £16.8m ($29.1m) per missile
Source: Federation of American Scientists
The government says it will decide whether to replace Trident before the next election and the Ministry of Defence says the move is "some way off".
Trident is expected to be decommissioned in 20 years' time. The nuclear deterrent system was last updated in 1980.
At the private meeting of Labour MPs on Monday evening, Mr Prentice called for a discussion paper setting out the options.
He also demanded a clearer timetable and a vote in Parliament.
Looking long term
Mr Reid said Labour had a manifesto commitment to retain the nuclear deterrent.
Trident was a minimum deterrent, he argued, and Britain would meet its obligations under the nuclear non-proliferation treaty.
The defence secretary said it was hard to predict the threats the UK might face in 15, 20 or even 50 years time.
While Mr Reid said no decision had been made, one of his supporters said he had put forward the soundest argument he had heard about why Britain needed to retain a nuclear deterrent.
A survey for the environmental group Greenpeace suggests more than half the British public opposes replacing Trident at a cost of £20bn.
It found 54% of people were against the idea, while 33% were in favour.
But when costs were not mentioned the result was closer, with 46% of the 1,016 people questioned by Mori opposed to replacing Trident and 44% in favour.
Greenpeace disarmament campaigner Dominick Jenkins said: "These poll results send a clear message to Tony Blair that a majority of the public oppose billions of pounds being wasted on building new UK nuclear weapons.
"The result indicates that people understand that with the Cold War over, nuclear weapons have no conceivable use and suggests that the public would support Blair taking a lead in getting rid of nuclear weapons worldwide."
A Ministry of Defence spokesman said: "A decision about any replacement for Trident is likely to be needed in this parliament, but is still some way off.
"Speculation about cost and types is therefore just that: speculation."