Former Economist editor Bill Emmott warned an audience of journalists that Gordon Brown would be "a meddler" in 10 Downing Street, during a talk reflecting on his 13 years' in the chair.
Emmott, who resigned from the current affairs weekly in February, also compared Tony Blair to a "gonzo journalist", in the event at the Frontline Club chaired by FT contributing editor John Lloyd.
Asked if he regretted his magazine's decision to support the Iraq war in 2003, he said: "Just looking at what was known at the time, I think between bad options — continuing a sanctions regime that had failed for more than 13 years and was causing misery to the Iraqi people or invading and causing further misery — on the basis of these terrible options it was right that we supported the invasion.
"The question is: should we have anticipated that the following three years would be run so incompetently, with too few troops to enforce security?
I still don't feel that on balance we could have known in advance that was the case.
"I think that I could make a parallel with some forms of journalism of which I don't necessarily approve.
"Fiction is written in an effort to convey what is believed to be true facts, and I think that is what the Government did.
"I don't think they lied directly about facts, but they lied about impressions. I do think Blair was sincere in his lying, in the sense that he believed he was representing facts that existed.
"It was gonzo journalism, yes: he believed he was representing the truth by lying. That, of course, is something that perhaps we should hold governments more accountable for than journalists — they have greater responsibility."
Suggesting Blair, like Thatcher before him, might prefer the leader of the opposition to his current deputy, he described Brown as "an inveterate meddler with all sorts of complications in the tax code".
He added: "He is an inveterate user of small changes to try to please particular interest groups and to grab headlines, and I think that particular instinct is a bad tendency, and not necessarily a good sign for the way he will run things in 10 Downing Street, if he gets there."
John Micklethwait, the former US editor of the title, replaced Emmott, who has announced his intention to write several books, his first on China and Japan.