Britain is prepared to scale back its nuclear arsenal as part of a drive to reduce the number of atomic weapons around the world, Gordon Brown announced yesterday.
The number of Trident warheads carried on the new fleet of submarines planned to protect Britain would be cut from 16 to 12 if other nations also agreed to reduce their nuclear stockpiles.
The Prime Minister argued the time had come for concerted action to stop more countries becoming nuclear powers and to tackle the danger of terrorist groups such as al-Qa'ida obtaining deadly weapons.
But he acknowledged that countries such as Britain, the United States and Russia also had to play their part by cutting back their nuclear defences.
"In Britain our operationally available warheads number fewer than 160 and the Government keeps this number under constant review," Mr Brown told a conference in London. "If it is possible to reduce the number of UK warheads further, consistent with our national deterrence requirements and with the progress of multilateral discussions, Britain will be ready to do so."
Two years ago, the Government took the unpopular decision to renew the country's Trident defence system at a cost of about £20bn. Although Mr Brown is determined to press ahead with the plans, he signalled that they could be reduced as part of a multilateral disarmament initiative.
He said: "We are committed to retaining the minimum force necessary to maintain effective deterrence.
"For future submarines, our latest assessment is that we can meet this requirement with 12 missile tubes, not the 16 on current submarines."
He said he hoped that talks next year between the nuclear powers would develop "a credible roadmap towards disarmament by all the nuclear weapons states".
Mr Brown added: "I know from President Obama and the new US administration that America shares with us the ultimate ambition of a world free from nuclear weapons."
But he suffered a setback yesterday when Dmitry Medvedev, the Russian president, announced plans for a comprehensive overhaul of the country's military machine. He said the aim would be to increase Russia's "combat-readiness", starting with "our strategic nuclear forces".
Downing Street played down the significance of President Medvedev's remarks. A spokesman pointed to "encouraging signs of a more constructive attitude" towards the issue on the part of the US and Russia, which hold 95 per cent of the world's nuclear weapons.
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