The announcement was made by the Foreign Secretary, Douglas Hurd, at the second day of the conference in New York on extending the nuclear Non-Proliferation Treaty (NPT), which came into force 25 years ago and is due to expire. Mr Hurd also noted previously announced decisions to abandon surface maritime nuclear weapons and to phase out Britain's free- fall atomic bombs.
Moreover, Mr Hurd for the first time pointed to the conditions under which Britain might enter its nuclear capability into a global negotiation for nuclear disarmament. "There is no doubt that a world in which US and Russian nuclear forces were counted in hundreds, rather than thousands, would be one in which Britain would respond to the challenge of multilateral talks on the global reduction of nuclear arms," he said.
The remarks, which have more symbolic than actual practical significance, were aimed at the large group of mostly non-aligned countries at the conference who are unhappy with the progress made by the five declared nuclear states - the US, Russia, China, Britain and France - towards disarming themselves since the NPT came into force in 1970.
While at least four of the nuclear states are pushing for an indefinite and unconditional extension of the treaty - the position of China is not clear - many among the non-aligned countries are expected to argue for its renewal only for a fixed or fixed periods. In that way they hope they can maintain the pressure on the five eventually to abandon their weapons.
There seems little doubt now that at least a slim majority will be found for indefinite extension when the conference concludes in about four weeks. However, Western diplomats stress that unless something close to a consensus of the participating states can be achieved, much of the moral force of the treaty, the centrepiece of all disarmament efforts, will be lost.
Urging indefinite extension, Mr Hurd said it would "underline to all - including those tempted to go down the route of proliferation - that the world community remains determined to prevent the spread of nuclear weapons and the horrors which this threatens. The treaty deserves the biggest vote of confidence we can give it." The Foreign Secretary said that Britain will have 21 per cent fewer nuclear warheads by the end of the decade than in the 1970s and their explosive power will be 50 per cent less. "If the world had seen cuts of this order in other types of weapons, it would be a safer and more stable place."
There is likely to be considerable scepticism about his presentation, however. In reality, Britain has barely been producing fissile weapons material since 1979, relying on recycling old warheads. Moreover, many in the non-aligned group are likely to question Britain's disarmament credentials against the background of its Trident submarine programme, which is only now just coming into force.
"The UK government is demaning an indefinite and unconditional extension on the basis of flimsy claims," Janet Bloomfield, chairwoman of the Campaign for Nuclear Disarmament said in New York. "It has a `do as I say, not as I do' attitude to nuclear proliferation."
Britain's continued reprocessing of plutonium for civilian use at the Thorpe reprocessing plant is also likely to be raised at the conference.