The inquiry on Monday continued its examination of post-war planning in the run-up to the Iraq war.
Major General Tim Cross, a senior British officer, said he urged Tony Blair to delay the invasion of Iraq two days before the conflict. Maj Gen Cross, who liased with the US on the aftermath of the invasion, told the inquiry planning for after the conflict was "woefully thin".
In the run up to the war, Maj Gen Cross was the UK representative to the Office for Reconstruction and Humanitarian Assistance (ORHA), the US agency responsible for drawing up plans for post-war Iraq.
He said that he met with then prime minister Tony Blair in February 2003, and told him of his concerns about the lack of post-war planning on both sides of the Atlantic. Although Maj Gen Cross said that Blair was "engaged", he said that he felt that there was "no coherent, single focus" on post-war planning across the government.
He said: "I do remember saying, in so many words, I have no doubt at all that we will win this military campaign. I do not believe that we are ready for post-war Iraq."
Maj Gen Cross subsequently worked for the Coalition Provisional Authority, which administered Iraq in the aftermath of the war.
Describing Iraq after the war, he said that he found the situation much worse than he had feared: "Baghdad was held together by chicken wire and chewing gum".
In the strongest criticism of the UK's failures in the reconstruction effort heard so far in the inquiry, he said that post-war planning was not taken "sufficiently seriously" in Whitehall.
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It has become very common for people to blame the Americans for all of this. I do just not accept that - Maj Gen Tim Cross
"We, the UK and we, Whitehall, should have done far more to get our minds round this issue," he said.
He added: "There was no minister of cabinet rank reporting back and driving this day to day. I stress that does not mean it was not there. It is just I never saw it."
Edward Chaplin, former UK ambassador to Iraq, told the inquiry that the UK government felt "helpless" when British citizens Ken Bigley and Margaret Hassan were taken hostage and killed.
He said: "They were terrible incidents. Terrible to the families, but terrible for the embassy, in the sense that we were very helpless. Kidnapping was very widespread at the time."
Chaplin said that the dysfunctionality of the new Iraqi regime, an interim government was set up in June 2004 under the leadership of prime minister Iyad Allawi, meant that it was difficult to track the whereabouts of the hostages.
He said that the government had been chosen "on ethnic and sectarian balance, rather than on competence to deal with the situation", adding that: "The other most striking thing was the sheer lack of capacity... to start the basics of government."
The government was in place until Iraq's general election in January 2005. Chaplin said that Allawi was in "a very difficult situation", and "showed a lot of personal and political courage in carrying out the job of prime minister."
Chaplin gave evidence to the inquiry last week about the build up to war and planning for its aftermath.