Bush says he will show the world the smoke on 5 February, when he unveils new evidence from US intelligence sources showing Iraq has illegal weapons. But the moment of truth will come on 14 February, when the UN Security Council is likely to decide whether to abandon fresh inspections in favour of military action.

The evidence of disarmament so far is mixed. Hans Blix, chief inspector for biological and chemical weapons for the UN Monitoring, Verification & Inspections Commission (Unmovic), told the council that Iraqi co-operation on process was good, but said it needed to improve its substantive co-operation.

'It is not enough to open doors,' he said. 'Inspection is not a game of 'catch as catch can'. Rather, it is a process of verification for the purpose of creating confidence.'

In terms of actual assistance, he said Iraq needed to allow inspectors to use monitoring aircraft and to encourage individuals to submit to private interviews with the inspectors, free from government intimidation. He also asked for more evidence to satisfy three key Iraqi claims: that it has destroyed 1,000 tonnes of VX nerve agent left over from the 1980-88 Gulf war with Iran; destroyed its anthrax capabilities; and does not possess long-range Scud missiles.

But Blix intimated that the onus was not only on Iraq to prove itself innocent, but on its accusers to help supply proof of infringement. 'Information provided by member states tells us about the movement and concealment of missiles,' he said. 'We shall certainly follow up any credible leads' - a clear request to the US to be more specific with its intelligence.

In summing up, the Swede noted Unmovic's strong capabilities, which he laid at the disposal of the Security Council in a coy bid for further inspections.

Mohammed Elbaradei, head of the International Atomic Energy Agency (IAEA), was more explicit. He said the IAEA had found no prohibited nuclear activities but needed months more to complete the investigation. 'Our work is steadily progressing and should be allowed to run its natural course,' he told the Security Council. 'We should be able within the next few months to provide credible assurance that Iraq has no nuclear weapons programme.'

If the inspections continue and fail to locate illicit weapons material, the UN will have to declare Iraq disarmed - triggering an end to the sanctions regime and the rehabilitation of Saddam Hussein's government. Weapons monitoring would continue under UN supervision. But would that be acceptable to the US?

There is an argument that the hawks are engaged in a game of bluff - making warlike noises to force Iraqi disarmament. After all, it is difficult to see Bush wanting to approach the 2004 presidential elections with US soldiers still propping up a new - and perhaps unstable - Iraqi government. And for Blair, there is strong opposition to war among much of the UK population, the British press and even his own political party.

But Bush has repeatedly made it clear that the war against Iraq and the war against terrorism are one and the same. 'Today, the gravest danger in the war on terror ... the gravest danger facing America and the world ... is outlaw regimes that seek and possess nuclear, chemical and biological weapons,' he said in the 28 January state of the union address. 'These regimes could use such weapons for blackmail, terror and mass murder. They could also give or sell those weapons to terrorist allies, who would use them without the least hesitation.'

At this stage of the war against terrorism, 17 months after 11 September 2001 and with little to show in the way of tangible victories - no Osama bin Laden, no Mullah Omar and no Ayman al-Zawahiri - Bush does not want to appear weak.

Under what conditions will Bush get support? On 29 January, the Security Council was scheduled to meet for preliminary discussions of the reports before a more serious meeting on 14 February. But the council is split. France, Russia and China have all made clear their belief the inspectors should have more time. The US and UK have said explicitly that this is Iraq's last chance.

The 31 January Bush/Blair summit at Camp David was expected to provide a common position based on US intelligence reports and moderated by the UK's more multilateral position. Early indications suggested the summit would result in a clear warning to Iraq that it must give immediate and complete answers to the weapons inspectors on all outstanding queries.

The crux of that position is likely to be the proof offered by Bush on 5 February to the UN. He claims that Iraq has illegal weapons and has been tricking weapons inspectors - making them ineffective. 'The inspectors have told us that they have evidence that Iraq has moved or hidden items at sites just prior to inspection visits,' said US Secretary of State Colin Powell on 27 January, dismissing the case for further inspections.

To back up its case that the inspections are futile and to provide wider support in the case against Iraq, the US will release intelligence covering Iraqi dissimulation. 'The US possesses several pieces of information, which come from our intelligence, that show Iraq maintains prohibited weapons,' said Powell. 'Once we have made sure it can be done safely, I think that in the next week or soon after we can make public a good part of this material.'

So far, such 'proofs' have been insubstantial. If Washington does want to use force, and if it wants a broad base of support to do so, it will have to produce more compelling evidence. Although it pushed UN resolution 1441 through a reluctant Security Council in October, it will be harder to get consensus on a final ultimatum.

If it fails to do so, Washington must either represent continued inspections as a triumph for the disarmament process or work outside the UN, possibly only with the UK in support. Bush's repeated dismissals of the inspections programme as ineffective have made the first option far harder to pursue without appearing to back down - a disaster in terms of domestic polling. The second option is, therefore, increasingly likely and the world should prepare itself for war.