The chancellor of the exchequer, widely expected to take over as prime minister from Tony Blair next year, waded into the debate over replacing Britain's submarine-based Trident nuclear weapons system.

The government is due to reveal its preferred option in December.

"People should bear in mind over the next few months on this issue that if North Korea has nuclear weapons, if there are other states threatening to have nuclear weapons, then it doesn't make sense to take unilateral action," Brown said.

"What we need is multilateral action," he told the Scottish Labour Party's conference in Oban on mainland Scotland's west coast.

"We have taken multilateral action since 1997. We've reduced the number of warheads, we've reduced the firepower of these warheads.

"We've taken action in the international community to promote multilateral disarmament and we will continue to do so."

Lawmakers will be allowed to vote on whether the government should replace Trident.

But members of the governing Labour Party will be expected to follow the party line -- despite more than 120 Labour lawmakers having lobbied ministers to give them a free vote, raising the prospect of another rebellion against Blair.

Trident has proved to be divisive issue between left-wing "old" and centre-left "new" Labour lawmakers under the pro-nuclear Blair, who became party leader in 1994 and prime minister in 1997.

Britain's current nuclear deterrent was set up in the 1980s when the Soviet Union -- not global terrorist groups such as Al-Qaeda -- was seen as the primary threat.

It is based on four Royal Navy submarines fitted with US-built Trident missiles which are due to become obsolete in the 2020s. One of the submarines is always on patrol.

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.

Replacing the deterrent is likely to cost anywhere from 10 billion to 25 billion pounds (19 billion to 48 billion dollars, 15 billion to 37 billion euros), observers say.

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