TONY BLAIR’s campaign to win public backing for a war on Iraq appeared to be faltering last night. The latest Populus poll for The Times showed that despite an intense campaign to drum up support, backing for the conflict was falling among Labour supporters, women and the professional middle classes.

The survey, undertaken between Friday and Sunday, underlines the huge task facing Mr Blair in winning over the public and suggests that he could not do so without a second United Nations resolution.

The poll is another blow to Mr Blair, as he tries to recover from the open show of defiance from Clare Short, the International Development Secretary, who promised on Sunday to resign unless he secured United Nations backing for war. Mr Blair’s personal position is being bolstered by Tory supporters, which is no consolation as he tries to contain a growing party revolt.

Labour’s support has fallen sharply since the autumn because of Iraq. As last month, the party is running level-pegging with the Tories.

By a two to one margin, the public does not believe the British and American governments have put forward a convincing case for war. Opposition has risen further over the past month, especially among women, only a quarter of whom now agree that a convincing case has been made (down from a third in February).

Like previous polls, the survey shows that public attitudes are closely tied to a second UN resolution.

About a half the public (52 per cent) agrees that Britain should join military action only if there is a new UN resolution. This compares with 62 per cent a month ago. This decline is largely because of a rise from 11 to 19 per cent in the number saying that Britain should join military action against Iraq regardless of whether there is a new UN resolution. But this is a small comfort for Mr Blair given the much larger number still offering only conditional support.

Iraq overshadows other political issues and continues to undermine Labour support. This is mainly because of a decline in the likelihood of Labour voters to turn out, rather than to abstain. The two main parties are still level pegging, at 34 per cent each. If sustained in the elections on May 1 to district councils in England and to the devolved bodies, Labour could face very sizeable abstentions from traditional supporters and therefore big loses of seats.

However, Mr Blair’s leader rating has improved over the past month and he is now ahead of both the other main party leaders. This reflects increased support both from Labour and, particularly, from Tory voters.

Ms Short meanwhile was attacked by fellow ministers and left twisting in the wind by Downing Street after her outburst on Sunday night.

Mr Blair had two telephone conversations, one before her interview was broadcast to discover precisely what she had said and another early yesterday in which he rebuked her for undermining his efforts to win a second resolution.

The Prime Minister considered sacking Ms Short for disloyalty but decided, after a breakfast meeting with his closest ministerial colleagues, that to do so would be a further distraction at a time when all his energies are concentrated on the UN. But Downing Street refused to give usual ritual assurance that Mr Blair had confidence in his minister, and there is a widespread view among ministers that if she does not herself resign her ministerial career will not go on much beyond the war.

Officials stonewalled all questions about Ms Short, saying that the Prime Minister was focused on winning a second resolution.

Mr Blair, questioned by women opposed to war on ITV1’s Tonight with Trevor McDonald, adopted the same tactic when asked about her threat to resign. He said: “My response is quite simply that I’m working flat out for a second resolution and the important thing at the moment is that we stay together and argue our case collectively.” It was a sometimes tetchy encounter for Mr Blair with a few of the 20 women slow-handclapping him.

Alan Milburn, the Health Secretary, Beverley Hughes, the Home Office minister, and many other Labour MPs condemned Ms Short for her timing. Her former No 2 at the International Development Department, said she had “pulled the rug” from under Jack Straw and Mr Blair.

Mr Blair and President Bush spent the day calling world leaders trying to win them round behind the second resolution.

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