The government was warned three years ago that the US post-war administration in Iraq was an "unbelievable mess", according to a leaked memo.
The US strategy in Baghdad was criticised in the memo
The memo was sent to Downing Street and the Foreign Office in May 2003 by John Sawers, Britain's senior official in Baghdad at the time.
It is included in the appendix of a new book Cobra II: the Inside Story of the Invasion and Occupation of Iraq.
Author Michael Gordon said Sawers was trying to "turn things around".
The memo included criticism of the US administration run by General Jay Garner, suggesting it was out of its depth, lacked leadership and strategy, and was inaccessible to Iraqis.
It included a warning over the security situation in Baghdad and that no progress could be made unless it improved.
BBC Security Correspondent Gordon Corera told Radio 4's Today programme the memo suggested how critical British military officials were about some US tactics. For example, he pointed to Mr Sawers' concern that every Iraqi civilian approaching a US check point was treated as a potential suicide bomber.
Corera added: "It is a jarringly and devastatingly frank picture of just how bad things were going early on. "
He said it was "snap-shot memo of a particular moment" but that the roots of a lot of the current problems in Iraq lie in those early failures.
The book's author Mr Gordon told the Today programme it was "well known" in the US that central command "really put all of their energies into major combat operations and on getting to Baghdad" and "did not do a good job on planning what would occur" in Baghdad afterwards.
He also defended General Jay Garner.
"To be fair to Jay Garner he was called into this process very late. That's not his fault, that's the Bush administration's fault," he said. "That said he didn't have a very effective operation."
Mr Gordon, who was an "embedded" correspondent with the US military, said at the time of the memo journalists were writing about "many of these problems" such as looting, an absence of electricity and the absence of law and order as well as the coalition not being well prepared to cope with these problems.
He said at the time these concerns were often dismissed as "the carping of journalists" by military spokesmen, but internally many diplomats had "as sobering a view as the journalists had".
Mr Gordon said after the war the US did not have enough troops to put on the ground to carry out patrols.
He said Mr Sawers suggested that Britain might send some troops to Baghdad to help.
He believed the envoy's aim was to alert the British government to some of the problems in Baghdad and try to force some action.
He added that Sawers: "Paints a picture of a coalition which is beginning to loose public support of Iraqis and his concern is to turn things around, and in fact in one of the memos he uses the phase 'three steps forward, two steps back'".