Speaking 48 hours before the Prime Minister’s audience at the Vatican, the Pope told an inter-religious delegation from Indonesia: “Neither the threat of war nor war itself should be allowed to alienate Christians, Muslims, Buddhists, Hindus or any other religion. All religions should strive for peace. War is always a defeat for humanity. It is a tragedy for religion.”

Mr Blair and his wife, Cherie, a Roman Catholic, will meet the Pope tomorrow for what Downing Street emphasises is a “purely private engagement”.

Although Mr Blair has told staff that he will not try to change the Pope’s mind during the audience at the Vatican, the question of Iraq is certain to be discussed.

There was dismay in London and Washington over the meeting between the Pope and Tariq Aziz, the Iraqi Deputy Prime Minister, who is a Christian.

Mr Blair has been struggling to win back the moral ground for war against Iraq after Britain’s leading churchmen cast doubt on his case yesterday.

Today Jack Straw, the Foreign Secretary, will argue that stripping Iraq of its weapons of mass destruction and defeating President Saddam Hussein is a moral policy. His speech to the Royal Institute of International Affairs will try to rebut an unusual joint statement by the Archbishop of Canterbury, Dr Rowan Williams, and the Archbishop of Westminster, Cardinal Cormac Murphy-O’Connor, who questioned the “moral legitimacy” of a military attack and gave warning of the “unpredictable humanitarian consequences”.

Mr Straw is to say: “In securing Iraq’s disarmament we will remove the threat Saddam poses to his neighbours and the wider world. We will effect a decisive shift in the fortunes of the long-suffering Iraqi people. And we will have reasserted the authority of the international rule of law.”

Referring to the conclusion of the Gulf War 12 years ago, he will say: “Iraq was found guilty in 1991. Twelve years of defiance later, they are not entitled to any presumption of innocence. Otherwise, Iraq will again use these terrible weapons. This is part of the moral case: preventing Iraq launching more wars of aggression, and dealing definitively with a tyrant who breaks international law.”

Mr Blair should find a sympathetic reception when he has talks today with Silvio Berlusconi, the Italian Prime Minister. Mr Blair wants to show a sceptical public that not only Britain is prepared to back President Bush on the issue.

He is hoping that Signor Berlusconi will repeat in public some of the arguments he used when he took on President Chirac of France over Iraq during Monday’s dinner at the EU summit. The Italian Prime Minister rebuked M Chirac during the latter’s lengthy oration about the risks of war, accusing him of ignoring the risks of not disarming Saddam.

Mr Blair’s “new Europe” tour continues next week with a trip to Madrid for talks with José María Aznar, his Spanish counterpart, another ally over Iraq and, crucially, a member of the UN Security Council.

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