The understanding is formally known as the 1958 Agreement for Cooperation on the Uses of Atomic Energy for Mutual Defence Purposes, but is usually called the Mutual Defence Agreement, or the 58 Agreement. It governs the two countries' trade in weapons of mass destruction. Trading in weapons of mass destruction is pretty controversial right now - given all the fuss about Libya, Pakistan, Iran and so on. But the negotiations between London and Washington are going on in secret, and the treaty is likely to be slipped in at the end of the year without anyone noticing.

Without the agreement, Britain would not have its Trident nuclear weapons system, or be a nuclear power at all. Britain has test-fired 24 hydrogen bombs in Nevada and, in return, supplied the US at times with plutonium. Britain continues to use Nevada for tests that don't involve nuclear explosion. For example, the UK conducted experiment Vito to check that a warhead would explode correctly on Valentine's day 2002.

The Trident nuclear warheads are dependent on the US. They are manufactured in Berkshire according to US designs and under management that includes the US arms producer Lockheed Martin. Specialist joint working groups include nuclear weapons engineering and manufacturing practices.

Neither Tony Blair nor George Bush has made any public statement about what deals are being struck over the renewal of the treaty, but they are likely to involve both specific technologies and political agreements. Tony Blair wants a successor to Trident supplied from the US. In return, the UK will help American WMD manufacturers where it can. For example, by doing some design work if Congress bars American firms from working on new weapons.

The broader political trade-off is likely to include support for Washington's military policies, which include: building new nuclear weapons; starting to test them again "if necessary"; putting non-nuclear weapons in space; and preparing anti-satellite weapons. All these programmes are under way in Washington.

There are more fundamental objections to the nuclear special relationship than signing up for the next round of Star Wars and H-bombs. The Mutual Defence Agreement encourages the British delusion that it is an independent nuclear power and therefore a force to be reckoned with. This self-deceit among British officials has been the greatest obstacle to any sensible discussion about Britain's foreign policy for half a century. And it relies on the full extent of the agreement being kept both from the public and even from almost all officials and politicians.

As with most dependent relationships, its defining characteristic is that nothing must be done to upset the controlling partner, so that partner gets more and more control. The CIA now often sits on the joint intelligence committee. So, even there, at the very heart of the British state, there is no independence of thought. You can be sure that the favour is not reciprocated.

The other side of the coin is that the agreement allows Washington to pretend to the American people that it has real allies even over reckless adventures such as the invasion of Iraq. But there, too, the truth is kept from the public and even from specialists. I only ever found a handful of defence advisers in Congress who had even heard of the programme.

Today, were the agreement to be debated, many Americans would oppose trading weapons of mass destruction with anyone, let alone the British. The moral majority that believes that gun control is tyranny, abortion the modern holocaust and gay marriage a threat to public order would not want to give America's precious nuclear secrets to a nation that is comfortable without its own guns, with a woman's right to choose and with human rights for gays.

Internationally, the US-UK trade in WMD sets a terrible example of double standards in which we are clearly arguing that our trade in WMD is good and other peoples' is bad.

Confronted with such huge issues, it is easy to think that there is nothing we can do. But pressure has made an impact before. Remember when France was blowing up nuclear bombs in the Pacific? Bill Clinton was pushing to get a nuclear test ban signed because it was popular. But the Tory government, with secret encouragement from some US officials, was opposed. When myself and other researchers told members of Congress about British obstruction, they threatened to cancel the cooperation agreement, John Major caved in, and the agreement went ahead. And so from 1996, for the first time since Hiroshima, neither Britain, China, France, Russia nor the US has been conducting nuclear tests.

So make a fuss and who knows, Congress might even decide to cancel the agreement. Without any extra pressure, there will be a couple of speeches by anti-nuclear MPs, and perhaps a secret discussion in the defence committee just before the treaty goes through. Since this agreement is supposed to be there to defend democracy, the government should have an adult conversation with the people about what is really involved.

· Dan Plesch's The Beauty Queens' Guide to World Peace is published in the summer by Politico's.

danplesch@aol.com

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