Short has continued to criticise Blair since her resignation
The way the UK and US prepared for war has resulted in chaos and suffering in Iraq, former cabinet minister Clare Short has said.
Ms Short said Iraqis were better-off without Saddam Hussein but "hurrying" to war on a fixed timetable meant not enough had been done to plan for post-war reconstruction.
Baghdad was now a "disaster" because the US Office of Reconstruction and Humanitarian Affairs (ORHA) had spent too much time on Iraq's future politics, she told BBC One's Politics Show.
That job should have been left to the United Nations while the coalition concentrated on securing order and humanitarian aid, she went on.
Ms Short claimed Tony Blair and US President George Bush had agreed on the date for war when they met at Camp David last September.
They had "duped" people into thinking the need for action was more urgent than it was, she said.
"We had more time. We could have done it properly and we could have tried without war, minimising the harm to the people of Iraq."
Ms Short continued: "Because all this was done secretly, the preparations for post-conflict were poor and we have got the chaos and suffering that we have now got."
The spin took away the time and created an urgency to get quickly to war
The former international development secretary said UK troops had done much better in restoring order in the southern Iraqi city of Basra than US troops had done in Baghdad.
"Baghdad is a disaster. Everything is wrecked. It is completely violent... The whole humanitarian system can't work because it's all so dangerous and disorderly."
The Birmingham MP said 12 years of UN sanctions after the first Gulf War had strengthened Saddam Hussein and caused suffering for the Iraqi people.
"That is why I did not support those who said containment is good enough.
"Yes, we should address the problem of [Saddam's] defiance of the UN and his war crimes, but we had enough time to do it well.
"The spin took away the time and created an urgency to get quickly to war."
Ms Short threatened to resign before the war, accusing Mr Blair of recklessness, but she decided to stay in the cabinet when the conflict began.
When she did quit, she said it was because the prime minister had broken his promises to her about the UN's post-war role.
Foreign Secretary Jack Straw told BBC One's Breakfast with Frost he was sorry Ms Short had made her latest allegations.
"I obviously appreciate why Clare should now be trying to argue that the original position she took was the justified one, not the subsequent position she took when she supported military action," he said.
He insisted the intelligence evidence about Iraqi weapons had not been "hyped" up at all.
Ms Short's words also failed to impress anti-war campaigner Tam Dalyell, the longest serving MP.
Mr Dalyell told BBC Radio Scotland: "Clare Short may well have been duped but the rest of us weren't."
He predicted electrifying consequences for Mr Blair if he were found to have deliberately misled Parliament.
He added: "I mean, bluntly, if it was a question of gullibility that is not a resigning
issue. If it was done on purpose then the House of Commons would have to come to
Conservative shadow foreign secretary Michael Ancram, who backed the war, said the government was "paying the price for not having given us information before the war started".
Mr Blair had to deliver on his promise to publish further evidence as soon as possible, said Mr Ancram, or the speculation would continue.
Liberal Democrat foreign affairs spokesman Menzies Campbell said only a special Commons select committee inquiry could end the "rumour and recrimination".