But Geoff Hoon, who was defense secretary in Prime Minister Tony Blair's government from 1999 until 2005, said intelligence officials had believed that Saddam Hussein was amassing weapons of mass destruction and that the allies did not lie about why they went to war.
In an interview with The Guardian newspaper, Hoon said that "we didn't plan for the right sort of aftermath."
"Maybe we were too optimistic about the idea of the streets being lined with cheering people. Although I have reconciled it in my own mind, we perhaps didn't do enough to see it through the Sunni perspective. Perhaps we should have done more to understand their position," Hoon was quoted as saying.
Hoon said the British side had not comprehended Cheney's influence in the U.S. administration.
Even when Blair and President Bush had agreed on some matter, "sometimes... the decision actually came out of a completely different place."
"And you think: what did we miss? I think we missed Cheney," Hoon was quoted as saying.
He did not cite any examples of decisions apparently reversed by Cheney.
Hoon, who is now minister for Europe in the Foreign Office, said Britain had opposed the wholesale dismissal of Iraq's army and police forces.
"We certainly argued against," Hoon was quoted as saying. "I recall having discussions with Donald Rumsfeld, but I recognized that it was one of those judgment calls. I would have called it the other way. His argument was that the Iraqi army was so heavily politicized that we couldn't be sure that we would not retain within it large elements of Saddam's people."
However, Hoon defended the decision to go to war on the basis of intelligence that believed Iraq was building up an arsenal of weapons of mass destruction — intelligence he now accepts was wrong.
"I've been present at a number of meetings where the intelligence community was fixed, and looked in the eye and asked are you absolutely sure about this? And the answer came back 'Yes, absolutely sure,"' Hoon was quoted as saying.
"I saw intelligence from the first time I came into office, in May 1999 — week in, week out — that said Saddam had weapons of mass destruction ... I have real difficulty in understanding why it was, over such a long period of time, we were told this and, moreover, why we acted upon it," he was quoted as saying.
"Whatever else I did, even if people say it was catastrophically wrong, I wouldn't agree with it, but I could live with it," he added. "But I can't live with the idea that I was telling lies, because I wasn't."
Hoon said he felt no need to apologize.
"You can say 'it did not turn out as we expected' and 'we made some bad calls,' but at the end of the day I defy anyone to go through what we went through and come to a different conclusion," he was quoted as saying.
The public, Hoon said, was not interested in perceptions in 2003 or subtle arguments over intelligence or policy.
"I think, especially when British soldiers are being killed, that the public have got to be pretty confident as to why. I think they're not any longer confident, and want us out of Iraq. That's why Tony gets the blame," Hoon said.