When Tony Blair was asked during the general election campaign about modernising Britain's nuclear arsenal he seemed almost puzzled that the question should be put. Of course Britain should retain a nuclear capability beyond the lifetime of its Trident submarines. Such was the prime minister's certitude, it seemed almost impertinent to ask why.

Gordon Brown, to whom as heir apparent the final decision may yet fall, took much the same tack. With a fleeting nod to the present review of the non-proliferation treaty at the United Nations, the chancellor remarked that: "The issue in the world is not whether the existing powers cease to be nuclear . . . I think the issue is whether we can prevent proliferation."