The two issues - his legal advice and the failure to find WMD in Iraq - are directly linked. We didn't go to war to topple Saddam; even the attorney balked at the legality of that. We invaded Iraq, according to Goldsmith, because Saddam had ignored successive UN demands that he abandon his WMD programme. The now discredited weapons dossier was used to back up the case.

We know from his published summary that just before the Commons vote on the war, the attorney argued that a second UN resolution was not, after all, needed. Goldsmith argued that the last one, 1441, had to be linked to 678 (passed in 1990) which authorised the use of "all necessary means" to get Iraqi forces out of Kuwait, and also to 687, banning the production of weapons of mass destruction.

That resolution 1441 authorised the use of force was - and continues to be - challenged by most international lawyers. In a nutshell, they say it was not enough to sanction military force. The resolution ruled out any "automaticity" (leading to the use of force) as the British and US delegates to the UN assured us.

Or as Lord (Peter) Archer, Labour's former solicitor general, told peers on the eve of war on March 17 last year: "resolution 1441... manifestly does not authorise military action. If the council had intended to do so it could have said so quite unambiguously. To seek to spell out such authority from a reference to "serious consequences" is to treat the security council as a delphic oracle."

That, I understand, was the gravamen of the Foreign Office legal advice before the war - a second UN resolution was needed. Elizabeth Wilmshurst, the FO's deputy legal adviser, resigned because she disagreed with the attorney's view. She was not the only one to protest, I am told.

A disturbing question in the whole affair is why Jack Straw, the foreign secretary, apparently dismissed the view of his own independent legal advisers, preferring to adopt the attorney's more comfortable, pro-war, approach.

Goldsmith, it appears, sent at least three separate pieces of advice to Blair between January and March last year and is believed to have had serious doubts about the legality of war without a second UN resolution. Indeed, his advice was sufficiently ambiguous in the run-up to the war for Lord Boyce, the then chief of defence staff, to demand "unequivocal" legal support for an invasion of Iraq.

More disturbing is that the advice of the attorney became more pro-war precisely at the time new intelligence came in saying that Saddam's WMD programme was not nearly as advanced as the government's September 2002 dossier claimed. Moreover, it suggested Iraq did not pose any threat, let alone an imminent one, to Britain or the US. It is inconceivable, sources say, that Goldsmith did not see this new intelligence.

As Sir Franklin Berman, former chief legal adviser to the FO, said in a letter to the Guardian, a decision to go to war is not like any other policy decision which may be taken merely on a balance of probabilities. We are talking here about military action that would not only visit death and destruction on another country but would overthrow the government of a sovereign state. Whatever one thinks of that government, the attorney dismissed a central principle in international law, that of proportionality, while at the same time ignoring the facts, ie, the new intelligence.

The prosecution last week dropped charges against the former GCHQ translator, Katharine Gun, knowing that the attorney's advice would be a key issue in the case. But it won't go away. Now protesters who entered the US base at Fairford are pleading that they, too, acted to prevent an illegal war and are demanding to see the attorney's advice.

Ministers say that publishing the attorney's advice would breach a long-standing "constitutional convention". Yet the advice of attorneys has been published before.

Lord Butler's inquiry covers the "use" of intelligence on WMD. There is no reason why that should not cover the use - or abuse - of intelligence by the attorney. Or is the prospect of questioning the legality of the invasion, and continuing occupation, of Iraq by British troops, too awful to contemplate? It could, after all, make British troops liable in both British law and before the international criminal court not only for the deaths of Iraqis in their occupying zone but for injuries and the destruction of property.