Sir Richard Dalton, Britain's ambassador in Tehran from 2003-06, has told the Chilcot Inquiry into the Iraq war that both the UK and US misread the intentions of Iran in the run up to the war.
Blair and Bush pushed the line that Iran would be hostile to the Iraq venture, when in fact Iran wanted the venture to succeed in order for a stable government to be formed and to ensure that US troops did not remain too long in the area.
Sir Richard said that Blair made "a series of very bad decisions" about the legality of the 2003 invasion.
Blair told Chilcot in January:
"What happened in the end was that they did because they both had a common interest in destabilising the country, and for Iran I think the reason they were interested in destabilising Iraq was because they worried about having a functioning majority Shia country with a democracy on their doorstep."
Sir Richard contradicted this:
"From what I saw of his evidence, I thought he very much exaggerated this factor."