John Rentoul: History may decide that invading was right. They just got the wrong country

There were not enough soldiers, and Blair shares the responsibility. At best he can say that he eventually gave Iraqis a sort of costly freedom

'Yes, they may. Then again, they may not." Thus the Foreign Secretary judiciously weighed the question put to her in a radio interview last week: Will historians come to judge the Iraq invasion as a foreign policy disaster? Margaret Beckett's reluctance to be more definite is understandable.

She knows that Tony Blair's reputation is sinking every time the political obituaries are rewritten for the day, coming some time in the next nine months, on which he finally announces his departure. For a while after the invasion of Iraq, it seemed possible that the verdict of history would be more generous than that of contemporaries. It couldn't go on getting worse, could it?

Now, the hope that it will all be all right if we give it long enough has faded. Eventually, Iraq may know better times. But it will take longer and cost many more lives than Blair could possibly have imagined. Historians are likely to ask themselves whether the invasion was a bad idea that was bound to go wrong, or a good idea badly carried out.

In one respect, Blair makes matters harder for himself by refusing to criticise the American post-invasion strategy. Provoked by heckling during his farewell speech to the TUC last month, he said that there was a reason for the suffering of the innocent in Iraq and Afghanistan, "and it is nothing to do with so-called failures of planning".

He may have been right to say that blaming the Americans for disbanding the Iraqi army is off the point - the army largely disbanded itself after the invasion. But the question of US and British troop numbers is relevant: there were not enough soldiers to prevent looting, secure the borders and safeguard weapons stores. That failure influenced what followed, as Iraqis looked to religious identities for security, forming sectarian militias.

That was a culpable error, for which Blair shared responsibility. Indeed, the experience in the "easier" south of Iraq does not support the idea that the British were significantly better than the Americans at managing the occupation. More troops initially may have helped, but that sectarian violence would still have become a problem.

The Prime Minister's last line of defence ought to be that the attempt to rebuild Iraq has gone badly - worse than almost anyone, pro- or anti-war, expected - but that the invasion was still the right thing to do.

At some point after he leaves office, he will have to accept that, although most of the killing in Iraq since 2003 is the "fault" of the people doing the killing, rather than of the US and British forces, it would not have happened without the invasion. His refusal to admit the scale of the disaster currently infuriates those who opposed the war, but historians are unlikely to be much more forgiving, even if the passions roused abate with time, which I doubt.

"Hardly anyone predicted it" is not much of a defence. Some people who knew what they were talking about did predict it, and historians will not give much credence to the impression Blair tries to give that sectarian militias sprang up without warning from nowhere. Equally, the fact that the ideologues of jihadism are wrong to portray the Iraq invasion as a war against Muslims does not cancel out the fact that it was predictable that they would.

However, on the question of whether the invasion was the right thing to do, the most important verdict has surely been given by the Iraqi people. They may, in time, decide that the whole venture would have been better not attempted. But that is not what they say now.

In January this year, a University of Maryland poll found that 77 per cent said ousting Saddam was "worth it", even when they were reminded of the "hardships you might have suffered since the US-Britain invasion". More recently, in an IRI poll in June, more Iraqis thought the country was headed in the right direction than the wrong one, and 60 per cent felt Iraq would be better in five years' time.

One problem is that history now knows that British service chiefs have lost confidence in the idea that they are helping to move Iraq in that direction. General Sir Richard Dannatt, the Chief of the General Staff, wants to get out because he thinks, on balance, there is little more that British troops can do. But again, surely, history should prefer the verdict of the democratically elected Iraqi government, which wants our troops to stay.

The big judgement that historians will be required to make, though, is what would have been the costs of allowing Saddam Hussein to remain. The difficulty is that this means speculating about what might have occurred. Yet there is some evidence of what happens if aggressive dictatorships are left alone, in the different shapes of Iran and North Korea.

One cabinet minister told me: "The anti-war argument that I do give credence to is that we took action against the wrong country. It should have been Iran." This is because Iran's nuclear ambitions - and sponsorship of jihadist terrorism - are more advanced than Saddam's were - a provocative way of saying that history may judge not that invading Iraq was wrong, but that it was not enough.

Certainly, the fashionable view today - that the Iraq invasion provoked the Iranians and the North Koreans to accelerate their nuclear weapons programmes - doesn't make sense. If the US had backed away from enforcing UN resolutions against Saddam, it would hardly have prompted Kim Jong-il and Mahmoud Ahmadinejad to say: "Oh, we'd better abide by the rules, then."

A more sophisticated version of the same criticism is that, by his support for an unpopular war identified with an unpopular President Bush, Blair undermined the prospects for a new doctrine of the UN having the responsibility to intervene in states' internal affairs to protect human rights. But would Britain really be intervening in Iran, North Korea and Darfur if we had stood aside from Iraq?

At best, then, Tony Blair can claim that he helped to stop a dangerous dictator from developing weapons of mass destruction, and that he helped give the Iraqi people a sort of costly freedom, eventually. The first should not be doubted, and historians may decide we were complacent about the threat of chemical, biological and nuclear weapons proliferation. On the second, Iraqis say it was a price worth paying, and why should historians contradict them? They may, of course. Then again, as Beckett might say, they may not.