Tony Blair last night used the rare opportunity of a historic address to the US Congress to declare that history would "forgive" him even if no weapons of mass destruction are uncovered in Iraq.
In a significant softening of Downing Street's stance on Iraq's banned weapons, the prime minister stood before hundreds of members of Congress to admit that he may eventually be proved wrong.
"Can we be sure that terrorism and weapons of mass destruction will join together?" the prime minister asked his audience of Republicans and Democrats, who are beginning to voice doubts about whether Saddam Hussein still possessed banned weapons in his final months in power.
Mr Blair then made a rare admission of fallibility: "Let us say one thing. If we are wrong we will have destroyed a threat that, at its least, is responsible for inhuman carnage and suffering. That is something I am confident history will forgive."
The prime minister's remarks, as he became the fourth British prime minister to address a joint meeting of Congress, will be seen as another watering down of Downing Street's previously tough stance on weapons.
Weeks after telling doubters in the Commons that they would have to eat their words, the prime minister signalled his change of heart last week when he declared that Britain and the US may only uncover a weapons programme, rather than actual weapons themselves.
With critics likely to seize on his admission, Mr Blair insisted that he still believed he would be proved right. "If our critics are wrong, if we are right as I believe with every fibre of instinct and conviction I have that we are, and we do not act, then we will have hesitated in the face of this menace when we should have given leadership; that is something history will not forgive."
The prime minister's address came as it emerged that the US has begun talks with other countries about establishing a new United Nations mandate for an international stabilisation force in Iraq. The US secretary of state, Colin Powell, said he had held talks with some foreign ministers about "whether or not it would be appropriate to start discussions about a UN resolution".
The almost daily deaths of American soldiers in guerrilla attacks and the waning of popular enthusiasm for the conflict has prompted the US to try to persuade other countries to share the burden of policing Iraq, but several nations are insisting on more explicit UN authority before they send troops.
US diplomats said that they had no plans to put forward a proposal of their own, but said that Washington was prepared to listen to ideas for a new UN resolution on a stabilisation force from other capitals.
US administrator Paul Bremer said last night that Iraq could hold its first free elections as early as next year. The exact timetable for elections would depend on how fast the new Iraqi governing council could write and ratify a new constitution.
Mr Blair's prediction that he would be forgiven by history was the highlight of a lengthy address to Congress. Aides are said to have "sweated blood" on the speech, which Mr Blair regards as one of the most important he has ever made overseas.
And Congress loved it. The prime minister received 19 standing ovations during his 32-minute speech.
After the first ovation, he joked: "This is more than I deserve and more than I'm used too, frankly." Watched by a roll call of America's great and good, Mr Blair received the strongest applause when he praised America for upholding freedom.
But a cross-party delegation of British parliamentarians struggled to join in the applause. Michael Howard, the shadow chancellor, found it most difficult to join the standing ovation.
The prime minister praised the US as a "light of liberty" in the world. But he used his platform to deliver an uncompromising message to both Europe and the US : that it is a two-way relationship in which both sides must be prepared to give ground.
He declared: "To be a serious partner, Europe must take on and defeat the anti-Americanism that sometimes passes for its political discourse. What America must do is to show that this is a partnership built on persuasion, not command." America must show that it is even-handed in the two areas of the Middle East peace process and the Kyoto protocol on climate change.
Praising President George Bush for his efforts in the Middle East, Mr Blair said: "I want to be very plain. Terrorism will not be defeated without peace in the Middle East between Israel and Palestine."
On the Kyoto protocol, Mr Blair attempted to woo the president to the cause of the environment by making an economic case. He said: "Climate change, deforestation and the voracious drain on natural resources cannot be ignored ... If this seems a long way from the threat of terror and WMD, it is only to say again that the world's security cannot be protected without the world's heart being won. So, America must listen as well as lead, but don't ever apologise for your values."
Mr Blair's toughest message was for the French president, Jacques Chirac, who he hinted wanted to turn Europe into a rival power to the US. He said: "There is no more dangerous theory in international politics today than that we need to balance the power of America with other competitive powers, different poles around which nations gather."
Mr Bush later lavished praise on Tony Blair for his "fabulous" speech. Speaking at a joint press conference at the White House, he said: "The prime minister once again showed the qualities that have marked his entire career. Tony Blair is a leader of conviction, of passion and of moral clarity. He is a true friend of the American people."
But Mr Bush spoke in more confident terms about the hunt for weapons of mass destruction, declaring that they would be uncovered.
18.07.2003: Tony Blair's speech to the US Congress
© Guardian Newspapers Limited 2003