Three years after the invasion of Iraq on March 20, 2003, and after a month of the worst violence since then, the Foreign Secretary acknowledged “misjudgments” after the war. But he stuck to the line that it was justified.

“We couldn’t have known then what we know now,” he told The Times, “given that intelligence turned out to be defective.” The view that Saddam Hussein “was a threat to international security was shared across the world”.

The “misjudgments”, he argued, were taken after the end of the war. “What we have learnt is that the post-war situation has been more difficult than we planned,” he said. “The planning for that was less satisfactory than it should have been.” The US-led coalition hadn’t understood that the “early euphoria had to be built on very rapidly. That didn’t happen quickly enough.”

He added that “I was worried at the time” about the scale of “deBaathification” — the decision to bar senior members of Saddam’s Baath Party from government jobs.

That was one of the first moves of Paul Bremer, sent by President Bush to run Iraq soon after the end of the war. It is now widely seen as a big mistake, together with the disbanding of the Iraqi Army. It stripped Iraq of experienced administrators, alienated moderate Sunnis and ensured that government and army were filled with Shias and Kurds. But Mr Straw argued that “we would still have faced a severe insurgency” from Sunnis, as “people who had to give up power were very angry”.

Are Iraqis better off now than before the war? “Yes,” Mr Straw said firmly, “but I understand why people are sceptical.” Since the February 22 bombing of the al-Askariya shrine, revered by Shias, Iraq has plunged into the worst violence since Baghdad fell.

It is politically paralysed; its first full-term parliament, elected in December, is riven with rows between Shias, Sunnis and Kurds, and has failed to pick a speaker, president, prime minister or cabinet. Yesterday, the parliament convened for the first time, in what should have been the climax of America’s vision. But it managed only 20 minutes of protocol to meet a constitutional deadline.

Some Shia leaders want Ibrahim al-Jafaari, acting Prime Minister, to stay. But others (and the coalition) have reacted with fury or dismay, finding him weak and partisan. Mr Straw, asked whether Mr Jaafari should step aside, said: “That is a matter for Iraqis.”

He added, smiling: “It is not confined to Iraqis, that someone nominated to prime minister wants to hang on to it — and that’s not a crime”.

He does think that Iraq’s eventual government “will be Western-leaning.” Will it recognise Israel? “That will take time, but if there is a move among other Arab countries to do so, then yes.”

Despite the deadlock, Mr Straw maintained that “Iraq faces an infinitely better future than if Saddam had been there.” He added the unusual argument that “you could have ended with full-scale civil war as his power waned” — that Shias would then have risen up. Does that mean that Iraq has a propensity for civil war? Straw does not accept that this is its fate. “The past three weeks have changed things, yes,” he said. “Five hundred poor souls have lost their lives.”

But he does not call this civil war, although he acknowledged that stories of communities dividing on sectarian lines are “a worry”. He added: “I’m reasonably optimistic that when you get a government, and it assumes responsibility for security, then they will start to rebuild society.”

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