The former chief UN weapons inspector Hans Blix has declared that the war in Iraq was illegal, dealing another devastating blow to Tony Blair.
Mr Blix, speaking to The Independent, said the Attorney General's legal advice to the Government on the eve of war, giving cover for military action by the US and Britain, had no lawful justification. He said it would have required a second United Nations resolution explicitly authorising the use of force for the invasion of Iraq last March to have been legal.
His intervention goes to the heart of the current controversy over Lord Goldsmith's advice, and comes as the Prime Minister begins his fightback with a speech on Iraq today.
An unrepentant Mr Blair will refuse to apologise for the war in Iraq, insisting the world is a better place without Saddam Hussein in power. He will point to the wider benefits of the Iraq conflict, citing Libya's decision to give up its weapons of mass destruction, but warn that the world cannot turn a blind eye to the continuing threat from WMD.
But, in an exclusive interview, Mr Blix said: "I don't buy the argument the war was legalised by the Iraqi violation of earlier resolutions."
And it appeared yesterday that the Government shared that view until the eve of war, when it received the Lord Goldsmith's final advice.
Sir Andrew Turnbull, the Cabinet Secretary, revealed that the Government had assumed, until the eve of war in Iraq, that it needed a specific UN mandate to authorise military action.
Mr Blix demolished the argument advanced by Lord Goldsmith three days before the war began, which stated that resolution 1441 authorised the use of force because it revived earlier UN resolutions passed after the 1991 ceasefire.
Mr Blix said that while it was possible to argue that Iraq had breached the ceasefire by violating UN resolutions adopted since 1991, the "ownership" of the resolutions rested with the entire 15-member Security Council and not with individual states. "It's the Security Council that is party to the ceasefire, not the UK and US individually, and therefore it is the council that has ownership of the ceasefire, in my interpretation."
He said to challenge that interpretation would set a dangerous precedent. "Any individual member could take a view - the Russians could take one view, the Chinese could take another, they could be at war with each other, theoretically," Mr Blix said.
The Attorney General's opinion has come under fresh scrutiny since the collapse of the trial against the GCHQ whistleblower Katharine Gun last week, prompting calls for his full advice to be made public.
Mr Blix, who is an international lawyer by training, said: "I would suspect there is a more sceptical view than those two A4 pages," in a reference to Clare Short's contemptuous description of the 358-word summary.
It emerged on Wednesday that a Foreign Office memo, sent to the Foreign Affairs Select Committee on the same day that Lord Goldsmith's summary was published, made clear that there was no "automaticity" in resolution 1441 to justify war.
Asked whether, in his view, a second resolution authorising force should have been adopted, Mr Blix replied: "Oh yes."
In the interview, ahead of the publication next week of his book Disarming Iraq: The search for weapons of mass destruction, Mr Blix dismissed the suggestion that Mr Blair should resign or apologise over the failure to find any WMD in Iraq.
But he suggested that the Prime Minister may have been fatally wounded by his loss of credibility, and that voters would deliver their verdict. "Some people say Bush and Blair should be put before a tribunal and I say that you have the punishment in the political field here," he said. "Their credibility has been affected by this: Bush too lost some credibility."
He repeated accusations the US and British governments were "hyped" intelligence and lacking critical thinking. "They used exclamation marks instead of question marks."
"I have some understanding for that. Politicians have to simplify to explain, they also have to act in this world before they have 100 per cent evidence. But I think they went further."
"But I never said they had acted in bad faith," he added. "Perhaps it was worse that they acted out of good faith."
The threat allegedly posed by Saddam's WMD was the prime reason cited by the British government for going to war. But not a single item of banned weaponry has been found in the 11 months that have followed the declared end of hostilities.
Mr Blair will argue that similar decisive action will need to be taken in future to combat the threat of rogue states and terrorists obtaining WMD.