Revelation emerges as government appeals against order to release minutes of two cabinet meetings in March 2003

Gordon Brown tonight faces fresh calls for an Iraq inquiry following the emergence of documentary evidence that "proved" there was insufficient cabinet discussions on the legality of going to war.

The revelation emerged in a court hearing today when the government was appealing against an order to release the minutes of two cabinet meetings, on March 13 and 17 2003, immediately before the start of the invasion.

Jonathan Swift, counsel for the Cabinet Office, revealed that it was part of the commissioner's case that the minutes of March 17 "proved the absence of sufficient discussion".

It is already known that at the second meeting, the then attorney general, Lord Goldsmith, gave the cabinet the single-page text of a parliamentary answer declaring that an invasion of Iraq would be legal without a further United Nations security council resolution.

Ten days earlier Goldsmith had given Tony Blair, then prime minister, longer and more equivocal advice, which was not shown to the whole cabinet.

Timothy Pitt-Payne, counsel for Richard Thomas, the information commissioner, said the commissioner was not suggesting that the minutes would answer "one way or another" whether there was sufficient cabinet discussion of Iraq as the issue had been discussed at many previous cabinet meetings.

The meeting on March 17 was the cabinet's only opportunity to discuss Lord Goldsmith's advice before the start of the war three days later.

Pitt-Payne said that he would discuss the exact contents of the minutes during a closed session, but he added that they were "highly material" to the issue.

The revelation appears to back up the claim of Clare Short, former cabinet minister, that she was prevented from questioning Lord Goldsmith on his opinion and whether he had any doubts.

Sir Andrew (now Lord) Turnbull, former cabinet secretary, told a House of Commons committee in March 2005 that ministers "had a chance to ask questions" following an oral presentation from Lord Goldsmith.

Last week, Lord Bingham, a former senior law lord, described the invasion of Iraq as "a serious violation of international law and the rule of law".

William Hague, shadow foreign secretary, today said: "The more we find out about how Britain went to war in Iraq the stronger the case grows for a proper inquiry into origins and conduct of the war.

"There is growing evidence that the decision to go to war was taken in the context of a serious failure of the machinery of government and of cabinet government. The good conduct of Britain's foreign policy requires the urgent restoration of both.

"The sooner we learn the lessons of the past the sooner we can apply them. So if this government persist in rejecting the inquiry the next Conservative government will establish one as an early priority."

The Liberal Democrat foreign affairs, Ed Davey, said: "This revelation is a damning indictment of Blair, Brown and the whole Labour leadership who sat round that table. No wonder Clare Short decided to leave the Labour party.

"Not to consider fully such a critical piece of legal advice, on the eve of a major war, makes a total mockery of cabinet government. Tony Blair broke the unwritten rules of our constitution, yet nothing has been done by Gordon Brown to prevent this happening again. "The case for a public inquiry has been strengthened yet again, and Gordon Brown should announce one in the Queen's speech." The tribunal concerns the records of cabinet meetings in March 2003, which considered legal advice on the imminent invasion of Iraq.

Thomas ruled earlier this year that the formal minutes of these meetings should be revealed. The Cabinet Office is currently appealing to the tribunal.