The survey, taken over the weekend, reveals that Mr Blair has sustained significant political damage from the debate over Iraq. His personal rating has dropped through the floor to minus 20 points, the lowest level since the petrol crisis two and a half years ago.
This month's Guardian/ICM poll also shows that at least one person from 1.25 million households in Britain went on Saturday's anti-war march in London, confirming estimates that between one million and two million people went on the march.
The poll shows it is the prime minister's personal standing rather than the Labour party which has suffered the wrath of anti-war voters. Labour's standing is down four points from 43% last month to 39% this month but the government still maintains a healthy eight-point lead over the Conservatives.
Opposition to the war has risen five points in the past month to 52%, with support for the war falling to 29%, the lowest level since the Guardian's tracker poll started last August.
Opposition is much stronger among women than men, with 59% of women saying they disapprove of a military attack on Iraq. Half of Conservative voters now clearly oppose the war but more Labour voters - 44% - still say they approve of military action than the 38% who are opposed.
Mr Blair faced further difficulties at the EU emergency summit in Brussels last night when Jacques Chirac insisted that France would veto a second UN resolution to explicitly authorise military action.
"There is no need for a second resolution today, which France would have no choice but to oppose," Mr Chirac said.
Jack Straw, the foreign secretary, appeared to be moving to the government's fallback position by repeating that though a new UN resolution was desirable, 1441 "gives us the authority we need".
Mr Blair, evidently irritated by France, Germany and others seeking to drag the process out, stuck to his guns, saying: "I think most people understand... if that [disarming] cannot be done peacefully, it must be done by force. That's why we require a timetable."
Earlier yesterday Mr Straw told the BBC that the government had to "take account of public opinion" and said that if a large part of the population opposes military action, it would be "very difficult indeed in those circumstances".
Later, his mood appeared to have hardened. "I don't think all the people on that demonstration - unquestionably the largest we've seen in my lifetime in the UK - would say that they represented alone British public opinion, but they certainly represented a very important element of it.
"But talking to people I know on that demonstration, some said to me that they were opposed to military action in any circumstances, others said they were worried about military action being taken prematurely but accept that military action may be necessary as a last resort - and that is the position of the British government."
In the French capital, meanwhile, a new poll showed that French public opinion had hardened against going to war. Eighty-seven percent were against military action, up from 77% six weeks ago, the Ipsos agency found in a poll for France 2 television conducted on Saturday.
· ICM interviewed 1,003 adults between February 14 and 16. Interviews were conducted across the country and the results weighted to the profile of all adults.
Alan Travis and Ian Black in Brussels
Tuesday February 18, 2003
The Guardian