Ambitions for reforming Iraq after the war were "probably higher than the ability to deliver", the former UK ambassador to the country has said.
Sir William Patey, in the job from 2005 to 2006, said there was no "quick fix" for changes such as setting up a police force and drafting a constitution.
The Iraq Inquiry heard that "what could be delivered on Powerpoint couldn't necessarily be delivered on Earth".
But the UK had not been "helpless or powerless", Sir William added.
During his time in office, Iraq was moving from a transitional government to full sovereignty, amid widespread schisms between different groups within the country.
Iraqi politicians were involved in drawing up a post-Saddam Hussein constitution, despite the fact that Sunnis had refused to take part in the process.
'Historical baggage'
Sir William recalled that he had written at the time that "the prospect of descent into civil war... was probably more likely than the transition to a stable Iraq unless certain things happened".
These included getting Iraqis involved in self-government and handling their own policing and security arrangements.