Mark Thomas pooh-poohs the plot to gas us

The government is trying to alarm you about terrorist attacks just as the weapons inspectors go into

You can tell that we are in the middle of a PR war on Iraq by one simple thing: it is now virtually impossible to buy a newspaper without a double-page pull-out-and-keep guide to potential terror threats. They normally come complete with an analysis of how a "dirty bomb" could affect London property prices and a fashion feature on "what's hot and what's not" in the world of gas masks. Meanwhile, Tony Blair manages the difficult trick of making the public more tense by telling everyone to try to carry on as normal, which has the calculated calming effect of Corporal Jones screaming: "Don't panic!"

Throughout the "Gas attack planned for London Underground!" articles that filled the papers this past week, it was conveniently forgotten that Tube and train passengers stand more chance of being killed in a rail crash than by a chemical weapon. Lack of investment, commercial pressures, failure to deliver automatic train protection, subcontracting maintenance work - all could play a part in the next train carnage. In the wake of the Potters Bar crash, Jarvis, the firm responsible for maintaining the track where the crash happened, claimed that someone had sabotaged the track. After the next disaster, whatever company is involved will no doubt claim to have seen Asians with prayer mats, AK-47s and large posters of Osama Bin Laden near the site.

At this point in time, there is more published, credible evidence to prove the existence of the tooth fairy than there is for the existence of a plot to gas the Tube. For Blair and his allies in the right-wing press (the Sunday Times, in this instance), it appears that what is relevant is not the facts, nor indeed any awareness of justice for the three men they fingered for the alleged plot. The real effect of the coverage, whether by design or by coincidence, is that fears about chemical weapons attacks are stoked just as the UN weapons inspectors go into Iraq. The end result is to link Iraq with public fears of being attacked; thus, it forms part of Blair's PR offensive* to convince us of the rightness of war.

For roughly 40 per cent of the British populace, the war on Iraq remains immoral, illogical and illegal. This is why on Tuesday 19 November, CND took action at least to begin to rectify one of those faults. They served letters on Tony Blair, Geoff Hoon and Jack Straw, warning them that they will face a legal challenge unless they give a written undertaking that the UK will not use force on Iraq without going back to the UN Security Council.

At first glance, this may not seem very important, but unless the government responds within seven days CND will take it to court.

This is hugely significant. It is the first time that a group of citizens is going to challenge legally its government's means of going to war. Sure, someone in the US may have taken their government to court over a war in the past, but Americans are so litigious that lawyers there have loyalty reward cards and you can collect frequent-litigant air miles. For the UK at least, this is a first.

Blair's government has been making qualified noises about how UN Security Council Resolution 1441 may be a legal mechanism with which to start military action against Iraq, but it knows it has to appear reasonable.

Geoff Hoon is an unlikely diplomat in these matters, looking as he does like a supply teacher who's just had six months off work due to stress-related illness. So it has been left mainly to Jack Straw to recite the government mantra that Britain will be bound by international law. However, legal opinion obtained on CND's behalf from Rabinder Singh QC and Charlotte Kilroy, both of Matrix Chambers, clearly shows there is no automatic trigger mechanism in the resolution allowing any country to use military action. In fact, the phrases from past resolutions on Kuwait and Bosnia that have been taken to mean military action are conspicuous by their absence in Resolution 1441, because the US and UK delegations fought to have those phrases included, but lost.

CND's legal action may force Britain to return to the UN to seek a clear resolution for military action. This move in itself does not stop the war against Iraq; nor does it justify the war if the UN tidies up its legal paperwork. However, at a time when reports predict half a million deaths from any conflict and its aftermath, we have a moral obligation to oppose the war with every tool available to us, and at least try to expose the lie of legality. Better that than roll over, do nothing and let the Sunday Times propaganda take its awful toll.

Donations to the CND fund to take the UK government to court can be made direct to the Co-op Bank, sort code 089033, account number 50425088.

* Please note that simple Iraqi people are subjected to propaganda, but sophisticated westerners are subjected to marketing campaigns and strategies