The government's top law officer has rejected fresh claims that his advice on the Iraq war suggested the conflict was illegal.

Lord Goldsmith was on Wednesday evening at the centre of fresh controversy over whether he thought the war might have been illegal.

There are also new questions over whether the attorney general's advice changed in the days leading up to the parliamentary vote authorising military action.

A document leaked to Channel 4 News and the BBC said that a second United Nations security council resolution authorising the war was the "safest legal course".

But in a statement to the Press Association, the attorney general said the document simply showed that he "took account of all the arguments before reaching my conclusion" that the war could be justified in international law.

Safest option

Sent on March 7, 2003 from Lord Goldsmith to the prime minister, the document says that relying on the first UN resolution, 1441, would need "strong factual grounds".

"I remain of the opinion that the safest legal course would be to secure the adoption of a further resolution to authorise the use of force," it adds.

"I accept that a reasonable case can be made that resolution 1441 is capable in principle of reviving the authorisation in 678 without a further resolution...

"However, the argument that resolution 1441 alone has revived the authorisation to use force in resolution 678 will only be sustainable if there are strong factual grounds for concluding that Iraq has failed to take the final opportunity [to disarm].

"In other words, we would need to be able to demonstrate hard evidence of non-compliance and non-cooperation."

Ten days after expressing caution about the case for war, Lord Goldsmith briefed the Cabinet and released a statement to parliament saying that the military action would be legal.

Lawful action

Reacting to the leak of his advice, the attorney general said that "far from standing up the case of the government's critics, [it] stands up the case the government has been making all along".

"Contrary to the allegations that have persistently been made, it does not say the war was unlawful but confirms the conclusion I reached was that a sufficient basis for the use of force was established without a second resolution," he said.

"What this document does, as in any legal advice, is to go through the complicated arguments that led me to this view.

"Far from showing I reached the conclusion that to go to war would be unlawful, it shows how I took account of all the arguments before reaching my conclusion.

"The document also makes it clear that the legal analysis might be altered by the course of events over the next week or so.

"Between March 7 and March 17, 2003, I asked for and received confirmation of the breach of UN security council resolutions.

"It was also necessary to continue my deliberations as the military and civil service needed me to express a clear and simple view whether military action would be lawful or not.

"The answer to the question 'was it lawful, yes or no', was, in my judgement, yes.

"And I said so to government, to the military, to Cabinet and publicly."

Full advice

The leak has again pushed the issue of Iraq and Tony Blair's conduct back to the top of the political agenda.

Michael Howard questioned what had prompted the apparent change of heart from the attorney general.

"It is now obvious from this legal advice that on March 7, 2003 the attorney general raised specific reservations about the legality of war in Iraq," said the Conservative leader.

"But Mr Blair has said that the attorney general's advice to the Cabinet on March 17 was 'very clear' that the war was legal, and that the attorney general had not changed his mind.

"It is obvious that he did. So what the public must now have an answer to is this: what, or who, changed the attorney general's mind?"

And Liberal Democrat leader Charles Kennedy called for full disclosure of the facts.

"We now urgently require a full public statement from the prime minister and the attorney general as to the events that took place over the 10 days in question," he said.

"The prime minister has always said the British people must make the final judgment on this matter and in the light of this revelation millions certainly will on May 5."