He has authorised officials to begin negotiations with Washington and with defence companies on the project before the cabinet or MPs have had the chance to debate it.

Reid has pleased service chiefs since taking over as defence secretary in May with his tough stance in standing up for the continuance of Britain’s independent nuclear deterrent.

He is said to want to maintain a British submarine-launched system because it is “invisible and invulnerable” to a potential enemy and can be swiftly deployed tactically anywhere in the world. His predecessor, Geoff Hoon, is thought to have been more willing to explore other options, such as a ground- or air-launched missile system.

The Ministry of Defence has been busily recruiting nuclear scientists to work at the Atomic Weapons Establishment in Aldermaston. Britain will build its own warheads, but the missile technology is likely to be shared with the Americans.

Officials have privately calculated that the costs of developing a replacement for Trident will start at about £500m a year, rising to an annual £1.5 billion, over the 20 years it will take to develop the system. Because of the length and complexity of the project, the prime minister must give official approval within the next two years.

The full cost of developing the Trident replacement is estimated to be £15 billion to £20 billion. Defence sources say this option is the most expensive because of the cost of maintaining the submarines.

Tony Blair told the Commons this month that “no decisions on replacing Trident have yet been taken, but these are likely to be necessary in the current parliament. It is too early to rule in or rule out any particular option”. But the prime minister has also said that it is “the right thing for the country”. Labour’s election manifesto said: “We are committed to retaining the independent nuclear deterrent.”

Ministers and MPs are likely to be concerned about the move to begin talks with the US and the defence industry before there has been a cabinet discussion or a parliamentary debate on the issue.

Since Britain acquired the American Polaris system in 1962, the country’s capability has been increasingly dependent on the US. Trident missiles are drawn from a common pool of weapons and equipped with British warheads.

Reid is said to have intimated to colleagues that after serving as defence secretary, a job he has long wanted, he expects to become the next foreign secretary. Such a promotion would put him in pole position to challenge Gordon Brown, the chancellor, for the premiership when Blair steps down.

Reid has been a prominent spokesman for the government on a range of issues, including the terror bombings on London. The defence secretary is believed to be one of the cabinet ministers who is urging Blair to stay beyond 2007 or 2008.

Reid has developed a rivalry with Charles Clarke, the home secretary, who has also been highly visible during the crisis.

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