But that figure was narrowly trumped by the 30pc who believe that Mr Blair's biggest legacy will not be the war, but the loss of trust in government engendered by his addiction to spin.
Of course, there is a fairly strong interrelationship between the two. I have always believed that what the public objected to most was not the war itself, but the way we were spun into it by Alastair Campbell and Co on the basis of dodgy dossiers and false prospecti.
But that only goes to demonstrate my main point - that the big, big problem with the Blair government - the one that has above all been responsible for its descent into public obloquy - has been spin.
There is no point rehashing it all again here. Blair will be gone in a few weeks, thank God, and to coin a phrase, now is the time to look forward, not back.
There now seems little doubt that Gordon Brown has the Prime Minsistership in the bag - but is he above the use of mendacious and misleading spin? For all that I admire the man, I'm afraid the answer to that is no.
Seven years ago, I covered a story for the Newcastle Journal in which Mr Brown attempted to spin away the existence of the North-South jobs divide.
Pointing to the fact that there were 75,000 people in the region claiming Jobseeker's Allowance and 61,000 Jobcentre vacancies, he argued that there were almost enough jobs to go round.
What the Chancellor was conveniently ignoring was the fact that his own Government had stopped using the JSA claimant count as the official measure of unemployment in 1998, and that the new ILO measure showed there were 103,000 people without jobs in the region.
Only The Journal and one other newspaper spotted this statistical sleight-of-hand, allowing Mr Brown's claim to go unchallenged in most of the national media.
Okay, so it's seven years ago now - fairly ancient history in political terms. So old in fact that no online version of the story now exists.
But if Mr Brown has become a changed character since then, it was not greatly in evidence during last month's Budget, when he foolishly attempted to present the 2p income tax reduction as a tax cut, which it wasn't, as opposed to a simplification of the tax system, which it undoubtedly is.
My view, and I suspect that of the millions of ordinary voters who have become disillusioned with New Labour over the past decade, is that all this must now end.
Whatever fresh policy directions Mr Brown intends to lead Labour in when he finally takes over, the biggest task facing the new premier is to restore public trust in government.
I don't believe that Gordon Brown will credibly be able to do that unless, like a recovering alcoholic, he can first acknowledge his own past dependence on spin and move on.
Can he do it? It may seem an extravagant claim, but I believe that on the answer to that question may well depend the result of the next general election.
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