Gordon Brown is preparing to surrender one of Britains four Trident submarines to help to cut nuclear arsenals around the world. The number and power of Britains 160 warheads could also be reduced. The Prime Minister will insist that scaling back the Trident fleet when the current programme is replaced has nothing to do with the economy but is instead part of efforts led by President Obama to slash nuclear stockpiles and force countries such as Iran to abandon efforts to build atomic weapons. It means that the future of Britains independent nuclear deterrent is in doubt whoever wins the next election. Liam Fox, the Shadow Defence Secretary, suggested recently that Britain scale back the Trident fleet from four vessels to three. This would raise questions about the effectiveness of the deterrent, given that one sub-marine is in base at all times. Mr Brown will signal tomorrow that he is ready to negotiate at a meeting of the UN Security Council on nuclear non-proliferation. It follows President Obamas decision to ditch the US missile defence shield in Eastern Europe. That move, and Russias delighted response, has bolstered hopes that a new non-proliferation treaty could be agreed next spring. Mr Brown has come under pressure to scrap Trident from those who claim that Britain can no longer afford its replacement, which will cost between 15 billion and 20 billion. Instead, he has opted to trim the platform. In doing so he would blur a potential dividing line with the Conservatives. Officials travelling with the Prime Minister to New York insisted that there was no question of surrendering Britains independent nuclear deterrent. They claimed that current advice from military chiefs was that a continuous at-sea deterrent could still be maintained with just three boats. Mr Brown is to insist that his offer is not related to the search by all parties for spending cuts. Aides say that neither the cost of building nor the cost of maintaining a slimmed-down fleet would be reduced by a quarter. His decision will disappoint Cabinet colleagues who had hoped that he might be willing to move to a cheaper air or land-based deterrent system. The final decision on the size of Britains next nuclear fleet will be taken after a recommendation by the relevant Cabinet sub-committee, expected before the end of the year. The replacement for Trident is not due to come into service until 2025, but key design decisions are required over the next two to four years. Although insignificant compared with US and Russian nuclear stockpiles, Mr Brown will argue that his offer would heap pressure on Iran to engage in a new treaty. The prospect of a grand bargain that offers states access to nuclear material for civil power in return for proof that no military programmes exist will feature strongly at the UN tomorrow. Industry sources told The Times that scrapping one of the four Trident nuclear submarines would not save a significant amount of money. If you build three instead of four it doesnt mean it will be cheaper, although overall there will be some savings, one source said. Key to the decision on cutting the fleet to three is the design of the new submarines. To prove that they will be as operationally effective as keeping four, the Ministry of Defence has had to show that the new boats could run for longer periods and have less need for refits and maintenance. It is estimated that replacing Trident with four submarines and extending the life of the existing Trident D5 ballistic missiles with an upgraded warhead would cost between 15 billion and 20 billion: up to 14 billion for the boats, plus 2 billion to 3 billion for refurbishing the warheads and 2 billion to 3 billion for infrastructure over the life of the submarines. The comparable cost for the first Trident system, with the four Vanguard Class boats, was 14.5 billion. The offer to go for three submarines will have a knock-on effect on the number of missiles and warheads purchased. The 2006 White Paper included a pledge to cut the number of operationally available warheads by 20 per cent. This left a stock of nuclear warheads of fewer than 160. BAE Systems is due to build the Vanguard replacement. It has more than 5,000 workers at Barrow-in-Furness in Cumbria devoted to sub-marine development and construction. It is currently building the Astute Class of nuclear-powered submarines. (The Times)