Mr Cook has resigned - but it is Mr Blair who is out of step with public opinion

Majority opinion in the country is unrepresented - not by the many MPs who would like to vote no - but by the party leaderships

Before the spin doctors get to work, let one thing be clear. Robin Cook's resignation yesterday is a big event. Conservative resignations on matters of principle or public policy are, oddly, much more common than Labour ones ­ Howe, Lawson and Heseltine are only recent examples. For a Labour resignation of even comparable seniority, you have to go back to Judith Hart in 1975. But although the triggering issue was also one of foreign policy, she resigned rather than accept a punitive demotion from the Cabinet.

If you except the, well, exceptional cases of George Brown and Frank Cousins, the last real parallel ­ especially if the vacillating Clare short does, finally, carry out her threat to resign ­ was the famous walk-out by Aneurin Bevan, Harold Wilson (both Cabinet members) and John Freeman in 1951 over NHS charges.

Mr Cook's resignation speech last night was, not unexpectedly, as good a case against this war as has yet been made in the Commons. He was especially good on the isolation over Iraq of the US and Britain compared to that in Kosovo, and of the corresponding vital importance of it being underpinned by a UN resolution. His clarion call to Parliament to stop the war will surely swell the ranks of the rebellion today. And while some dissidents will surely return to the government fold, there are others who will have decided, quite reasonably, that there was no point in voting against the Government while Mr Blair was toiling to secure the second UN resolution that was for so many in the party ­ and the country ­ a precondition of support for war, but that they would do so if war was decided on without a UN resolution. But even if the second group were to outnumber the first to the extent that Tony Blair had to rely on the official Opposition as Ted Heath did on the vote on joining Europe in 1972 (admittedly on a free vote), the policy would still survive.

But while yesterday's resignation may not be as destabilising as those in 1951, it differs from most Labour resignations since then in one fundamental sense. Which is that the resigner, though essentially a man of the left, goes more with the grain of public opinion, on this issue, than the Government he is leaving. Which brings us to the Conservative Party.

For one of the little passing mysteries on the eve of today's debate is just why it is that not only the Government but an Opposition struggling to increase its popularity should pass up yet another opportunity to represent middle opinion in the country. You don't have to deny the almost heroically principled, albeit misguided, way in which the Tory leadership has determined to stick by the US whatever it does, to recognise that it need not have been like that.

For a start, they might have allowed a free vote in their own ranks; some estimates are that as many as half the Tory backbenchers might have joined the Labour dissidents had they done so. But supposing that at the last Iraq debate, or even earlier, they had put down an amendment saying something along the lines of "This House regrets that the Prime Minister has not yet been able to persuade the British public of the case for war," then it might have united most Tory hawks with most doves in all parties.

A cheap parliamentary trick? Perhaps. But no cheaper than Labour's tactics, approved by a Shadow Cabinet containing the present Prime Minister, Chancellor and Foreign Secretary, during the Maastricht debates. A trick of which Iain Duncan Smith presumably approved, since he routinely trooped through the Labour lobbies in support of just such procedural devices at the time.

It's too late of course. Any change in Conservative tactics of supporting the Prime Minister would now look far too cynical. But what this little flight of fancy illustrates is that, save for the Liberal Democrats, a minority party, majority opinion in the country is so underepresented, not by the sum of MPs ­ who, left to their own devices, might vote no today ­ but by the party leaderships.

There is more in this, I think, than the natural distaste for war in every democratic population. For it has two features special to the present crisis. First, it is no doubt true that President Chirac has strengthened Tony Blair's position by his determination to veto the draft resolution abandoned yesterday. And although the French have not been as opposed to war under any circumstances, as Washington and London have claimed, the French President may well have overplayed his hand, helping the US to destroy the last vestige of UN unity without preventing a war. But no amount of blame for French intransigence can disguise the fact that a British foreign policy failed in New York yesterday. It just may be that this will be eclipsed by a military success and the consequent benefits to the Iraqi people optimistically outlined in the Azores on Sunday. But the British failed to bridge the gulf between old Europe and the US as they had sought to do. I can remember a senior British diplomat back in November pretending to do the splits to illustrate the difficulties of simultaneously persuading the French that if they accepted UN resolution 1441, a second would still be needed to sanction war, and the US that it wouldn't. Maybe this was a caricature even at the time; but it illustrates the larger truth that Mr Blair was unable ­ not, of course, for want of valiantly trying ­ to deliver Europe to the US or to lock the US into the UN and its inspection process, as he had tried to persuade Europe he would do.

And, secondly, what informs mainstream concerns about an Iraq war is not so much fear of increased terrorism, valid as that may prove to be, or squeamishness about war per se. The bafflement and scepticism is about the new doctrine that lies behind pre-emptive, regime-changing war, especially when it does not have the explicit sanction of the UN, the one body that can guarantee some measure of international stability in such potentially destabilising circumstances. That doesn't make pre-emptive war wrong. It may be that the new and emerging transatlantic doctrine of systematic intervention in totalitarian-terrorist and failed states, powerfully outlined in a new Foreign Policy Centre pamphlet by the writer John Lloyd, will be proved right for our times. But Mr Cook was at his most persuasive last night in suggesting that Iraq will be a dangerous, and in human life, costly test case for such a doctrine.

No one can be sure that this hugely risky experiment, for that is essentially what it is, is going to work. But the times are much too grave for opponents of war to hope to be proved right. The one certainty is that we must hope this war, launched to an inexorable US military timetable, will succeed without the death toll eloquently envisaged by Mr Cook last night. And that a talented politician should be congratulated for acting in accordance with his convictions.

d.macintyre@independent.co.uk