Both the British and American governments got just about everything wrong in their assumptions about what would follow the fall of Saddam, reports John Ware in the second of two articles linked to a new TV series.
As Iraq has collapsed in bloodshed and chaos, in recent months a "blame game" between London and Washington has been opening up.
There was no clear post-war plan for governing Iraq after Saddam's fall
At issue is the failure to plan properly for what would follow the invasion.
There was looting and anarchy almost as soon as the statue of Saddam was toppled back in April 2003.
The Americans hadn't prepared for this - even though a power vacuum always follows the overthrow of a regime almost as night follows day. The insurgents soon filled it.
What added fat to the fire, according to Lord Jay, Permanent Secretary at the Foreign Office during the invasion, were the first Orders issued by Paul Bremer, the newly appointed head of the Coalition Provisional Authority.
CPA Order Number One on 16 May 2003 was a radical purge of the Baath party: the revolutionary movement that had propelled Saddam to power and helped keep him there.
Lord Jay says the order was too radical: "...there were real risks in removing from the administration really right down to quite a low level people who'd been members of the Baath Party, because they hadn't been a member of the Baath Party because they were particularly fond of Saddam Hussein, they were members of the Baath Party because they wanted a job."
On 11 May 2003 - five days before the Order - the government's special representative to Iraq, John Sawers, [now Sir John as UK ambassador to the UN], sent a message to London headed "What's Going Wrong" stressing: "We need a clear policy on which Baathists can return."
CPA Order Number Two on 23 May 2003 announced the formal disbandment of the 400,000 strong Iraqi army.
General Sir Mike Jackson, then head of the British Army, has blamed disbandment for driving unemployed trained soldiers into the arms of the insurgents.
In his recent autobiography, General Jackson says: "To what extent the government communicated our concerns to the Americans I have no idea."
No clear policy
General Sir Mike Jackson blamed disbandment for driving insurgency
The answer appears to be that when ministers and officials had a golden opportunity to press their concerns a few days before Mr Bremer issued both orders, they didn't take it because they still hadn't settled on a clear policy either on the Baathists or on what to do with the 400,000 soldiers who'd been employed in Saddam's army.
On 13 May 2003 - two days after Mr Sawers impressed on London the need for one - senior officials from the Ministry of Defence, Foreign Office, Home Office and the Department for International Development met Bremer's security adviser Walter Slocombe.
Also present were two Cabinet ministers: Baroness Amos, the newly appointed Secretary of State for International Development, and the Defence Secretary, Geoff Hoon.
Mr Slocombe's cable back to Washington says: "UK briefed on their (admittedly not fully developed) thoughts on security sector reform, which they see as including de-Baathification."
The cable adds: "UK people raised issues of ex-soldiers as potential source of trouble" to which Mr Slocombe's response was that he didn't think the new Iraqi army that was to formed should be "expected to sop up unemployment."
However, it also stressed: "If some UK officers or officials think we should try to rebuild and reassemble the old regular army, they did not give any hint of it in our meetings and in fact agreed with the need for vigorous de-Baathification, especially in the security sector."
If some UK officers or officials think we should try to rebuild and reassemble the old regular army, they did not give any hint of it in our meetings
Former US security adviser
Mr Bremer tells the BBC programme: "None of them raised any concerns about the intention not to recall the army."
When I asked Mr Bremer if that meant the British government was "fully on board with both de-Baathification and the disbandment of the military," he responded: "And beyond that they said to him they recognised and again I quote: 'That the demobilisation of the Iraqi army is a fait accompli.'"
Mr Hoon was still supporting disbandment in Parliament six months later by which time the insurgency was well under way.
Asked on 3 November 2003 by Tory MP Crispin Blunt if he agreed that disbandment of the army was a "serious blunder," Mr Hoon replied: "No, I do not think that it was a serious mistake."
However, last May Mr Hoon told the Guardian newspaper that the government had "certainly argued against" both disbandment and de-Baathification.
When I asked him how he reconciled both statements, Mr Hoon said it was probably fairer to say that he'd had "an exchange of thinking" with the US defence secretary and the Pentagon on disbandment before the invasion.
"We took the view that the Republican Guard could be a force for stability. We were told they were good professional soldiers. Not necessarily fanatically loyal. The Americans were much more of the opinion that it was a Saddam-led organisation. It could never create stability."
He explained that he'd told Parliament that he hadn't thought disbandment was a serious mistake at the time because the consequences were not then apparent to him: "If I had known then what I know now, I would have taken a tougher line with the Americans and would have argued more strenuously because it became clear that the insurgency was becoming more professional."
Rush to war
Although John Sawers had urged on London the need for a clear policy "on which Baathists can return", Jay Garner, the retired American general whom Mr Bremer had just replaced as civilian administrator in Iraq, says Mr Sawers was a "big supporter of de-Baathfication" and also a "big supporter in getting rid of the army."
The Americans suspect there's some ex post facto rationalisation going on in the "blame game" over Iraq on this side of the Atlantic.
The truth is both governments got just about everything wrong in their assumptions as to what would follow the fall of Saddam.
The reconstruction of Iraq was the biggest project of its kind since the American General George C Marshall planned for the reconstruction of Germany after World War II.
Marshall got three and a half years to do it. Both London and Washington only put their planning units in place about eight weeks before the invasion.
The evidence suggests that in the rush to war, planning for what came afterwards was not a first order priority in either Washington - or London.
The second and final part of "No Plan, No Peace" is on BBC One at 2245GMT, Monday 29 October
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