The Cabinet Office is to conduct a new assessment of alternatives to Britain's Trident nuclear deterrent in a fresh concession to the Liberal Democrats, it was announced today.
Defence Secretary Liam Fox said the design of a new generation of missile-carrying submarines, together with £3 billion of initial contracts, had been agreed ahead of the final decision on replacing the existing fleet due in 2016.
However he told the House of Commons that while he still believed that a submarine-based ballistic missile system remained the most effective deterrent, he had agreed that officials should look at the alternatives.
"The coalition agreement reflected both parties' commitments to a minimum credible nuclear deterrent, but also the desire for the Liberal Democrats to make the case for alternatives," he said.
"To assist the Liberal Democrats in making their case for alternatives I am also announcing today the initiation of study to review the costs, feasibility and credibility of alternative systems and postures."
He said that the study would be carried out by officials in the Cabinet Office under the supervision of the Lib Dem armed forces minister Nick Harvey.
The move marks a further concession to the Lib Dems who have already succeeded in putting back the "main gate" decision on placing the final order for the submarines to 2016, after the next general election.
Dr Fox said he remained convinced that only a like-for-like replacement for Trident could provide a credible deterrent.
"If we want to see a minimum credible nuclear deterrent for the United Kingdom, the system that will be provided by the replacement Trident system is the best and in fact the only credible one," he said.
Dr Fox said the decision to order "long lead" items would ensure that the first of the four replacement submarines would enter service in 2028 as planned.
He said the real-terms cost of the programme remained at the £11 to £14 billion set out in the 2006 White Paper under the former Labour government, although inflation meant it had risen in cash terms to £20 to £25 billion.
Greenpeace said that Dr Fox's approval of contracts worth £3 billion gave the lie to Liberal Democrat boasts that they had delayed a final decision on Trident until after the next general election.
Official documents obtained by the environmentalist group through a Freedom of Information request reveal that the Ministry of Defence is due to buy a series of components for Trident replacement submarines ahead of the final decision, because of the long lead-time needed for their production.
The items included steel for the submarine hull and structural fittings; primary and secondary propulsion systems; electrical generation, conversion, and distribution systems; and components of the combat systems.
Louise Edge, head of Greenpeace's disarmament campaign, said: "Nick Clegg said there would be no replacement of the Trident nuclear submarines in this Parliament but today his Government committed billions of pounds to doing just that.
"If he's not to break his promise, Nick Clegg needs to step in and stop taxpayer money being spent on Trident replacement by the back door."
Shadow defence secretary Jim Murphy said: "Britain's independent deterrent has been the cornerstone of our peace and security over half a century and our view is that in today's world, as long as there are other countries with such capability, it is right that the UK retains an independent nuclear deterrent.
"In 2007, Parliament supported an independent continuous-at-sea nuclear deterrent. It is crucial that a review of that decision is evidence-based and in the interests of national security, not driven by the dynamic within the coalition parties.
"We welcome the announcement to proceed to Initial Gate, but there are big questions for the Government to answer. It is still unclear why there has been a delay and how much this will add to costs. We need to know from which budgets the total cost of the replacement will be met.
"Maintaining the UK independent deterrent must be part our continuing to lead global multilateral disarmament efforts."