CHANNEL 4 News last night broadcast details from a document it claimed was the Attorney General's secret advice to Prime Minister Tony Blair about the legality of war in Iraq.

The programme said that the contents of the document, drawn up by Lord Goldsmith on March 7, 2003, differed sharply from the summary of his opinion given to MPs on the eve of war ten days' later.

The document warned that British troops involved in any invasion of Iraq might face prosecution in the international courts and said that the safest legal course would be to secure a new Security Council resolution authorising war, Channel 4 News reported.

And it said that Lord Goldsmith believed that the UK and US would need strong factual grounds and hard and compelling evidence of Iraqi breaches of United Nations resolutions before taking military action.

There was no immediate response to the broadcast from Downing Street.

Channel 4 said the document addressed the question of whether the UN Security Council's Resolution 1441 provided authorisation for military action if Saddam Hussein failed to co-operate with weapons inspectors.

According to the document, Lord Goldsmith believed that the wording of the resolution left it "unclear" whether it authorised war.

"In these circumstances, 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 continued.

The advice said that "a reasonable case" could be made that resolution 1441 permitted the use of military action, based on the revival of the Security Council's resolution 678, passed at the time of Iraq's 1990 invasion of Kuwait.

But it added: "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."

Tory leader Michael Howard said: "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?"