The history of Britain’s nuclear deterrent is a long and not particularly glorious one. In the 1940s Churchill gave up trying to develop Britain’s own atomic bomb and sent scientists to collaborate with the Americans. Harold Wilson’s 1964 Labour government came to power having rejected Polaris in its manifesto but carried on with it anyway. A decade later Labour secretly pushed through the Chevaline programme to develop a new Polaris warhead.

The current state of Britain’s nuclear deterrent looks, on the face of it, like tokenism. Only one of the four Vanguard-class submarines that carry Trident nuclear missiles is at sea at any one time and, since the 1998 strategic defence review, those missiles are in shutdown mode, requiring several days’ notice before they could be fired. Many will say this is right, given the nature of the post-cold war threat. As we report today, however, work on Trident’s replacement is well under way, even before a political decision has been made on it.

Should Britain have a nuclear deterrent, let alone a new one costing billions of pounds? Michael Portillo, a former defence secretary, argued here last year that Tony Blair should call time on Britain’s era as a nuclear power. “The Soviet Union collapsed long ago,” he wrote. “There is no threat from China. The new nuclear weapons’ states, from India to Israel, do not have the capability to hit us.” Far better to spend the money on other defence needs, he argued, and shelter under America’s nuclear umbrella.

The Foreign Policy Centre, which has Mr Blair as its patron, says in a new report that discussions over Trident’s replacement are based on the false premise that Britain has an independent nuclear deterrent. Not only do we depend on America for the supply of weapons but there could also be no question of using them without US consent. In the unlikely event that a British prime minister wanted to press the button, America has the political power and the technology to stop it happening.

So why not get rid of them? The first argument is about Britain’s place in the world. Put crudely, would we really want to hand France the role of being western Europe’s only nuclear power? The nuclear deterrent gives Britain a place at the top table that it would be loath to surrender. Nor does the argument that Britain is in nuclear terms the 51st state cut much ice. Harold Macmillan acknowledged that more than four decades ago and his successors have accepted it. In some respects America would prefer it if Britain did not have its own deterrent. While we do, there is at least a chance of exerting influence.

More important than this is the nature of the world into which we are moving. The threat from the Soviet Union may have gone but the danger of “loose nukes” getting into the hands of terrorists or rogue states has increased. When Michael Foot proposed unilateral nuclear disarmament in the 1980s, the enemy was clear. Today that enemy is more difficult to identify, but may well come to include countries such as Iran and North Korea. To abandon our nuclear weapons in the naive hope that regimes like this will respond in the same way would be folly.

Nobody wants nuclear proliferation. The Trident replacement will be designed and brought into use in a way that respects the comprehensive test ban and nuclear non-proliferation treaties. What we do need, however, is a decent public debate. John Reid, the defence secretary, has promised this but it has yet to take place. He will doubtless say that the Trident replacement work going on at Aldermaston, Los Alamos and the Lawrence Livermore laboratory in California does not prejudge the political decision on whether to proceed. That may be so, but it creates suspicions of a backdoor move, as with nuclear power, on which we have had tantalising hints from the prime minister but little more. There is a strong case for Britain to maintain a nuclear deterrent. The government should be making it.