Now Blair cites regime change as basis for war. So, was it legal?

Tony Blair shifted his grounds for going to war in Iraq yesterday when he said that Saddam Hussein's humanitarian record had tipped the balance in favour of military action against him.

Tony Blair shifted his grounds for going to war in Iraq yesterday when he said that Saddam Hussein's humanitarian record had tipped the balance in favour of military action against him.

Mr Blair told the Commons that he was convinced a stand needed to be taken on weapons of mass destruction in Iraq and al-Qa'ida's training ground in Afghanistan had to be removed. He said: "And though in neither case was the nature of the regime the reason for conflict, it was decisive for me in the judgement as to the balance of risk for action or inaction."

He told MPs: "I am proud of this country and the part it played, especially our magnificent armed forces, in removing two vile dictatorships and giving people oppressed, almost enslaved, the prospect of democracy and liberty."

His statement represented a shift of ground after spending months studiously avoiding using the desire to topple Saddam as a justification for war.

Until now, the Prime Minister and other senior cabinet ministers have relied instead on the threat posed by Saddam's plans to acquire weapons of mass destruction to justify the war. They have shied away from the overt concept of "regime change" - one of the reasons cited repeatedly by President George Bush - except as a means of securing Saddam's disarmament.

In the crucial Commons debate on the eve of the war, Mr Blair said: "I have never put the justification for action as regime change."

It is believed that Mr Blair would not have won the green light from Lord Goldsmith, the Attorney General, to go to war for humanitarian reasons. He approved military action on the grounds that Iraq was in breach of United Nations Security Council resolutions on WMD.

After the failure to find any WMD in Iraq, Mr Blair began to make a retrospective argument for regime change, arguing that the world was a better place for the Iraq war. In September last year, for example, Mr Blair said Iraq was "the right thing to do" because "if we succeed in putting Iraq on its feet as a stable, prosperous and democratic country, then what a huge advertisement that is for the values of democracy and human rights, and what a huge defeat it is for these terrorists who want to establish extremist states".

Mr Blair went further than that yesterday in what was seen a part of an attempt to "shift the goalposts" away from WMD. Peter Kilfoyle, the former defence minister, said: "There is no doubt that he changed his ground. He is talking about something that is outside international law. He has learnt nothing."

Last week, Mr Blair conceded for the first time that such weapons might never be found in Iraq. However, before and after the war, ministers have stressed the human rights abuses and tyrannical nature of the Saddam regime. Mr Blair has also frequently pointed to discoveries of mass graves in Iraq and challenged his critics to declare that they would like to see Saddam back in power. Jack Straw, the Foreign Secretary, has also claimed the war was a "just cause".

In the Commons debate on the eve of war, Mr Blair said: "We must face the consequences of the actions that we advocate. For those of us who support the course that I am advocating, that means all the dangers of war. But for others who are opposed to this course, it means - let us be clear - that for the Iraqi people, whose only true hope lies in the removal of Saddam, the darkness will simply close back over. They will be left under his rule, without any possibility of liberation - not from us, not from anyone."

The Government also encouraged the work of the Labour backbencher Ann Clwyd, now the Prime Minister's special human rights envoy to Iraq, who was instrumental in briefing Labour MPs before the crucial vote on military action in March last year.

Senior Labour backbenchers, led by Ms Clwyd and Clive Soley, former chairman of the Parliamentary Labour Party, have forcefully argued that Mr Blair boxed himself into a corner by relying on weapons of mass destruction to justify war.