Moves to replace Britain's nuclear submarine fleet are "highly premature", an American expert has told MPs.
Trident is a submarine-based nuclear weapons system
Tony Blair says a decision has to be taken now to develop new submarines carrying the Trident missiles, as they are due to be decommissioned in 2024.
But Richard Garwin, who worked on the design of the first hydrogen bomb, said they could keep going into the 2030s.
"I think the government is hastening into this decision before the facts are really available to it," he said.
Mr Blair has said it would be "dangerous" for the UK to give up its nuclear weapons and wants to develop a new generation of submarines.
He said even if their working life is extended by five years, it will take 17 years to design and build new craft.
MPs will vote on the plans in March.
But Dr Garwin told the Commons Defence Select Committee that US Trident submarines, which spend more time at sea than their UK equivalents, had had their lifetime extended to 45 years.
TRIDENT MISSILE SYSTEM
Missile 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
"I would expect that the UK submarines, from the point of view of wear-out, would last 100 years," he said.
"I see no reason why they shouldn't last 45 years."
Dr Garwin has advised the US government on national security since the 1950s and chaired the State Department's Arms Control and Non-proliferation Advisory Board.
He said the submarines' steam generators would not keep going for 45 years, but could easily be replaced, much more cheaply than the £15-20bn the Ministry of Defence estimates the new vessels will cost.
Liberal Democrat defence spokesman Nick Harvey said Dr Garwin's comments added weight to his party's position.
"We must not rush to a decision just to secure Blair's political legacy. The wise and cost-effective solution is to take a final decision only when it becomes operationally necessary," he said.
Campaign for Nuclear Disarmament chairwoman, Kate Hudson, added: "We strongly encourage MPs to question the urgency of the Government's decision.
"Any decision made now will commit the UK to possessing nuclear weapons for many decades to come."