Only a full inquiry can avert another disaster like Iraq

The two main opposition parties will make another valiant effort today in the House of Lords to persuade the government to hold an inquiry into why its pre-war analysis of Iraq was so badly wrong. Valiant, because several previous attempts, including in the Commons, have failed.The last try came close. The government defeated a motion by Welsh and Scottish nationalists by just 298 to 273 votes. That was in October 2006, and the then foreign secretary, Margaret Beckett, used the spurious argument that an inquiry could send a dangerous signal to insurgents that Britain did not have the determination to stick it out in Iraq. It was the worst kind of macho plea: "Don't give aid and comfort to the enemy", an unmerited claim of security in order to censor discussion.

The Beckett argument, even taken at face value, doesn't hold water. Britain has abandoned its military positions in central Basra in the year and a quarter since she spoke. Its remaining troops are huddled at the airport. They play only a minimal role. For Britain to hold an inquiry into the government's Iraq deliberations of 2002 and 2003 will make no difference to the safety of the last 2,500 troops still there.

The government's other argument is that there have been at least four Iraq inquiries already: the Hutton inquiry, the Butler inquiry, and hearings by two parliamentary select committees. True, but they focused on only one part of the story - the accuracy of the intelligence on Saddam Hussein's alleged weapons of mass destruction and the way Downing Street used it.

There has been no inquiry into the equally important issue of the political intelligence circulating in Whitehall about the consequences of an invasion, how Iraqis would react to an open-ended occupation by US and UK forces, and the strong possibility that the post-Saddam vacuum would be filled by Islamists, some with close links to Iran, rather than the secular, pro-western exiles favoured by Washington and London.

Some critics complain the government made no plans for how to run Iraq. But the main failure was for Bush and Blair to think they could run Iraq. Kanan Makiya, the Iraqi exile whose powerful book about Saddam's atrocities, Republic of Fear, helped to fire up Bush and the neocons, came to that view recently after much agonising. A passionate advocate of invasion, he now says, "The first and the biggest American error was the idea of going for an occupation".

If the US and British government's most controversial pre-war decision was to go to war after ignoring the will of the UN security council, their behaviour after the invasion was as badly flawed. Instead of handing Iraq to UN peacekeepers or, better still, to Iraqis themselves to choose their government, George Bush and Tony Blair persuaded the security council in May 2003 to adopt resolution 1483, authorising a prolonged occupation. By then, sadly, the war's strongest opponents, France, Germany and Russia, seemed exhausted by their pre-invasion battles with Washington. There was also relief that Saddam had been toppled relatively quickly. The anti-invasion troika had little stomach to go on resisting Bush, beyond the important limit of refusing to contribute their own troops to the quagmire into which they rightly expected the so-called multinational force to sink.

Why was none of this foreseen in Whitehall, particularly by the Arabists of the Foreign Office and MI6? Or did they sound warnings which were not listened to? It would be nice to think the latter was the case. My research suggests otherwise. Government experts predicted that Iraq could become a magnet for al-Qaida, but seem to have been as ill-informed as ministers about the social and political changes going on beneath the heavy lid of Saddam's tyranny. They did not predict resistance from Iraqi nationalists, nor spot the growing strength of Iraq's Islamists, both Sunni and Shia. Cabinet ministers say they saw no position papers on the likely politics of postwar Iraq. My recent interviews with FCO diplomats in office at the time produced no evidence that accurate analysis even reached the foreign secretary.

Perhaps my informants did not know the whole story. Some members of the earlier generation of FCO Arabists have expressed surprise at the apparent lack of expertise among their successors. Others point to the absence of a British embassy in Baghdad since 1991, so that by 2003 the corps of officials with experience of Iraq was tiny. Some complain budget cuts have reduced the FCO's policy planning teams. Crisis management has replaced strategic thinking. Others talk of the Downing Street monopoly of decision-making on big issues, which began with Thatcher, and a culture of civil service subservience - "give the minister what he/she wants to hear and don't raise difficulties".

The only way to get the truth is to have a full-scale inquiry. What did the government's experts really do? Why didn't they go beyond Whitehall and regularly consult specialists outside? What questions did ministers ask? How an inquiry should be conducted - in public, partly in private, by privy counsellors or a select committee - are matters for debate. The crucial issue is that the government must open itself up to scrutiny.

This is not the stuff of some history PhD. Invading and occupying Iraq has been the greatest British foreign policy blunder since Suez. If the mistake is not to be repeated, we need to know how it happened, and we need to know it now.

Jonathan Steele. His book, Defeat: Why They Lost Iraq, is published today.