Britain is likely to decide before 2010 whether to replace its Trident submarine-launched nuclear-tipped ballistic missile system, which comes up for renewal in around 15 years.

The hearing gave proponents on both sides of the argument the chance to set out their case as part of the decision process.

Sir Michael Quinlan, a former top Ministry of Defence official, told the Commons Defence Committee into the British nuclear deterrent that it was unclear how much a replacement system would cost.

"How much risk we are prepared to accept," he asked, against an unspecified future threat.

"My own view is that there will be some cost that will be simply too much to pay for the insurance of staying in this business."

He favoured scaling back Britain's deterrent, but said it would be a wrench to give nuclear weapons up -- particularly while France kept theirs.

"I think it is just national gut feeling," he said.

"To leave the French as the only people with (a nuclear deterrent, out of Britain and France), I think, would twitch a lot of very fundamental historical nerves.

"I am not arguing about the logic of it. I just think there will be that gut feeling that we can't."

Lee Willett, of the Royal United Services Institute military think-tank, warned against giving up Britain's nuclear weapons as other countries acquire them.

He said: "We do not know what the future will hold. While others have nuclear weapons, the only thing that will deter a nuclear weapon is a nuclear weapon."

Rebecca Johnson, of the Acronym Institute for Disarmament Diplomacy, dismissed the concept of nuclear deterrence.

"If you believe in it, then it gives you a bit of reassurance until it gets tested and it fails, at which point it is far too late to discover that it wasn't actually helping you at all," she said.

Britain has four Trident submarines in service. They each have 16 multiple warhead nuclear missiles with a range of 12,000 kilometres (7,500 miles).

If ministers do decide to replace Trident, they would have to choose whether to stick with a purely submarine-based deterrent or utilise land- or air-based systems.

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