I have weapons of mass destruction at the bottom of my garden. They glide through the loch encased in the sleek black belly of a massive Vanguard class submarine. Each sub houses 16 missiles with three warheads on each. The warheads in turn contain 100 kilotons of explosive material; in civilian speak, eight times the payload of Hiroshima.

These are not nice boats. As the parliamentary debate on their replacement approaches, people are much exercised by the financial arithmetic. Figures from £25bn to £76bn are quoted, depending on whether maintenance costs are factored in.

These are not cheap boats. They are called our independent nuclear deterrent. Only one of these words bears much scrutiny. They are, indeed, powered by a nuclear reactor. Independent? The missiles are made and stored in Georgia US and we have them on a puchase/lease from the Americans. The manuals used by our navy are American. Nobody thought it necessary to anglicise the spelling. The exercise, after all, is more technological than grammatical. And politically, perhaps technically, it is unthinkable that they could be used unilaterally.

A deterrent? To whom? A terrorist planting an explosive device in an urban transport system? A suicide bomber halfway to paradise anyway? Don't take my word for it. Two former US Secretaries of State, George Shultz and Henry Kissinger, with former Defence Secretary William Perry and former Armed Services Senate Committee chair Sam Nunn, have just examined the case for a new generation of nuclear weapons. Nuclear weapons were essential during the the Cold War, they wrote in the Washington Post.

Now, they say "reliance on nuclear weapons for this purpose is becoming increasingly hazardous and decreasingly effective". They call nuclear weapons the ultimate means of mass devastation, and note that non-state terrorist groups play by no tidy rules of engagement. They urge America to reassert a vision of a world free of nuclear weapons; to work towards that goal rather than add to the proliferation that would "dramatically increase the risk that nuclear weapons will be used".

These are hardly soggy liberals. Yesterday, two men who would be Prime Minister tried to outbid each other with greener-than-thou speeches. Both are persuaded of the desperate danger that climate change might bring about the end of the world before their young children have a chance to inherit it. It might. With nuclear war there is no might about it. The nuclear non-proliferation treaty is a game of two halves. The first urges non-nuclear powers to stay that way. The second places an obligation on pre-existing ones to work for disarmament and reduce their own arsenals.

A Trident replacement puts us legally and morally beyond that pale. The chief scientist at Aldermaston lets the cat out the bag on his website, admitting that the £350m per year for three years being spent on its upgrade will ensure the development of warhead design "including the ability to provide a new warhead . . . most of our research is conducted in this area". So much for successive Defence Secretaries insisting the funds were for refurbishment and maintenance of the status quo. So much for the Prime Minister's assertion that the decision will be taken "in a far more open way" than ever before. These are not honest men.

This week our elected representatives have a clear-cut opportunity to honour our non-proliferation pledge and to try, despite our role in Iraq, to assert some moral leadership. An opportunity to put an end to the muddle-headed hypocrisy which rails against nuclear ambitions in Iran and North Korea, having conveniently averted our eyes from the development of nuclear weaponry in India and Pakistan while conniving in the ludicrous pretence that Israel doesn't have any.

That is one route. The other is to spend money we can ill afford building weapons we could hardly dare use against threats we can hardly predict or define while giving tacit encouragement to every tinpot dictator to do likewise. The notion that we need nuclear weapons to keep the peace is ludicrous. Nobody suggests we give teenage gangs sub-machine-guns on the grounds that the consequences of using them would preclude anyone having an itchy trigger finger. And the post-cold-war world more resembles undisciplined gangs scrapping over territorial rights than a statesman-like quadrille around the negotiating table.

Do nuclear weapons make the world a more dangerous place? Without a scintilla of doubt. Does our deciding now to upgrade ours make it the more combustible? Absolutely. Would such a move encourage further proliferation in unstable regions such as the Middle East? Undoubtedly.

Is a Labour government, supported by a Conservative opposition, to be allowed to hurry us faster along the road to Armageddon?

We will find out tomorrow.