Mr Blair would be wise not to ignore the unease over his Iraq policy

It wasn't difficult, listening to the debate, to imagine circumstances in which the rebellion would be much more widespread

It's quite easy to dismiss Tuesday night's parliamentary rebellion on Iraq. Although at the upper level of expectations, it did contain many of the kind of people you would have expected to vote against the Government on many issues.

There are several reasons, however, why Tony Blair shouldn't be complacent about the unease exposed by the debates in the Commons – and, virtually unnoticed but every bit as instructive, in the Lords on Tuesday. For a start, nothing like all those who expressed deep reservations (from Labour's Chris Smith to the especially cogent Tory dissident Douglas Hogg) voted. Which isn't surprising, since important – and overdue – as the debates were, they were taking place before the crisis point had been reached.

It wasn't difficult, listening to the debates, to imagine circumstances in which the rebellion would be much more widespread. War is still a probable hypothesis – and war without UN sanction only a possible one – rather than a certain reality. In these circumstances many, perhaps even most, of the doubters understandably saw no point in protesting against a circumstance that has not come to pass and may just still be avoided.

Secondly, political management is not quite the same as conclusively winning the national argument. Blair was on top form on Tuesday. He has seized back a command of the debate that seemed to be slipping away in the summer. He was convincing in arguing that while regime change was both desirable and probable, the destruction of his arsenal and not the removal of Saddam would be the casus belli if war happens. He was equally in command of the Cabinet at a meeting on Monday. It began with a storming defence of government strategy by John Prescott and, by all accounts, an unequivocal statement of support by Gordon Brown. More striking still, Robin Cook, who has hardly made a secret of his reservations, is said by those present to have been fulsome in his praise of Blair's handling of the crisis so far.

Blair's argument to the potential dissenters, including to Clare Short in his 20 minute tête-a-tête before the cabinet meeting, has been simple and effective: if what you want is to forestall war, remain united in backing the threat of war. Only then can Saddam be persuaded to give the unfettered access to the inspectors that may prevent it being carried out.

More broadly, the Cabinet supports him – for now – partly because it knows that he has brought George Bush to the UN, and that Blair is pushing the Americans with increasing robustness to restart the Middle East peace process – though without much result so far – both for its own sake and to meet the paramount concern of the Arab countries; and partly because it thinks his strategy could yet succeed. In politics, nothing succeeds like success.

This doesn't mean – as Blair almost certainly knows – that he has dispelled all the widespread doubts of many with no reason to oppose him for the sake of it. And these are not merely the doubts of politicians. In a questioning and thoughtful speech on Tuesday, the former Foreign Secretary Lord Hurd (beside revealing that in 1990 the Foreign Office and the State Department prevailed over a reluctant No 10 , still under Margaret Thatcher, and White House to seek UN Security Council backing for the Gulf War) said he had never known "a time when so many people have been interested but uncertain" about a great issue; complete strangers came up to him in the street or on the train to ask: "What's going to happen about Iraq?"

This public concern, underlined by the polls, demonstrates that the new preference for pre-emption over deterrence isn't just an issue for global strategists. Many who believe instinctively in war in response to an identifiable act, or acts, of external aggression find it much more difficult to accept the idea of a democracy starting a war, against however wicked and dangerously armed an enemy. Embedded in the collective memory is the idea that the Second World War, the first Gulf War and Kosovo, which were in the first category, succeeded, and Suez, which was broadly in the second, wasn't. Blair hasn't yet quite succeeded in removing that doubt.

That doesn't mean that a war against Saddam can't be justified, or that Blair did not go a very long way to doing so on Tuesday. But it does underline the crucial importance of discussions, currently reaching a climax in New York, aimed at UN backing for an enforceable ultimatum to Saddam. Differences did open up between the US and the UK. The Blair Government's role as a bridge between the US and its other allies has never been more tested. It wants a tough, clearly enforceable resolution – but also one that is acceptable to the other permanent members of the Security Council. It has even looked ominously possible that the US would produce a resolution of its own that the UK would not co-sponsor and that the French and Russians might regard merely as a precursor to regime change. However much Britain would argue publicly for its acceptance, that would be a tell-tale sign that Blair had failed to secure a resolution that he thought could command real international support. Washington and London may reach agreement on this after all, but it is a sign of how tough negotiations have been.

At a Policy Network seminar 10 days ago, Blair was asked, by the former French finance minister Dominique Strauss-Kahn, about his approach to Iraq and its differences from that of other European governments. Strauss-Kahn warmly acknowledged Blair's success in persuading the US at least to try the UN route of delivering an ultimatum that Saddam could accede to if he chose, but then asked: "Will America do it right?" Replying, Mr Blair was at his most persuasive in arguing for engagement with the US. Only with the help of the world's only superpower was there any chance of fulfilling "a comprehensive international agenda" from Kyoto to ending Aids, famine and war in Africa, from relieving world poverty to achieving a just settlement in Israel-Palestine. But to the specific question posed by Strauss-Kahn, he gave no answer. Not, it is safe to assume, because he wouldn't, but because he couldn't.

It remains the only question that matters. If America does it right, allowing the UN Security Council to give Saddam one genuine last chance, backed by the credible threat of force if he doesn't take it, it's still possible that the widespread doubts about the deep dangers of a pre-emptive war that surfaced in Parliament on Tuesday, and are present among much of the public, can be contained. If it does it wrong, insisting on a UN resolution that it knows France and Russia won't accept and is really no more than a flimsy pretext for a war it has already determined on, then it will pose Tony Blair a terrible dilemma. And if he resolves it by promising to back the US in just the kind of unilateralist war he never himself wanted, then Tuesday night's rebellion could start to look like a walk in the park.

d.macintyre@independent.co.uk