Top legal officer 'changed mind on Iraq attack'

He said that until February 2003 – just a month before the invasion – he believed specific authorisation for war was needed from the United Nations.

But he changed his mind after meeting senior figures in former President George Bush's US administration in Washington.

Just one month after he personally presented his advice to Mr Blair that he would require a further Security Council resolution if he wanted Britain to join a US-led invasion, he returned to No 10 to tell the Prime Minister's senior aides it was not necessary.

"I did reach the view then – and still am of the opinion – that it was lawful," he said.

"It was an opinion that I reached independently having considered all the arguments and the evidence and that was my genuine view."

He disclosed that, despite having recommended a second resolution would have represented the "safest course", he had no hesitation in issuing a straightforward statement on the eve of invasion that military action was lawful.

He said the way he expressed his earlier view had been "overly cautious" but he strongly denied he had been asked by Mr Blair to change his opinion.

He first raised his concerns about the legality of military action against Iraq with Mr Blair in July 2002 as the Prime Minister was preparing for talks with Mr Bush.

He said he made clear the UK could not rely on earlier United Nations Security Council resolutions dating back to the 1991 Gulf War and a fresh mandate was needed.

When, in November 2002, the Security Council passed resolution 1441 requiring Saddam Hussein to give up his supposed weapons of mass destruction, he still did not regard it as a sufficient basis for the use of force.

On January 14, 2003, as British troops were preparing to leave for the Gulf, he presented a draft legal opinion to Mr Blair advising him a further Security Council resolution would be required.

But the No 10 chief of staff, Jonathan Powell, arranged for him to meet Britain's UN ambassador, Sir Jeremy Greenstock, and the American negotiating team.

Lord Goldsmith said his meeting with Sir Jeremy on January 23 helped to sway his opinion that the wording of 1441 could in itself justify military action.

"Sir Jeremy, on his own, had some good points. He moved me in my mind but he didn't quite get me there," he said.

What clinched it was his meeting with the Americans in Washington on February 10. His main discussions were with the State Department legal adviser Will Taft, although national security adviser Condoleezza Rice also "dropped in".

Two days later, in discussion with his legal assistant in London, he finally came to the conclusion a second resolution was not necessary.

On February 27, Lord Goldsmith returned to No 10 to inform Mr Powell and Mr Blair's foreign policy adviser Sir David Manning of his new opinion.

"I told them that...I was of the view that a reasonable case could be made that a second resolution was not necessary and that was, on past precedent, sufficient to constitute a green light," he said.

He then formally set out his view in a lengthy written opinion given to Mr Blair on March 7. At that stage he was still advising that the "safest course" would be to obtain a second resolution.

But, with negotiations in the UN close to break down, he was then approached by the chief of the defence staff Admiral Lord Boyce and the Treasury solicitor Dame Juliet Wheldon asking for an unequivocal assurance that military action was legal.

"I very quickly saw that actually this wasn't satisfactory from their point of view," he said.

"They deserved more. Our troops deserved more, our civil servants who might be on the line deserved more than my saying there was a 'reasonable case'.

"So therefore it was important for me to come down clearly on one side of the argument or another, which is what I proceeded to do."

The inquiry was adjourned until tomorrow when Mr Blair will give evidence.