A test of the effectiveness of the new law will be whether it can secure disclosure of the circumstances of the most important Government decision of recent times: to join the United States in invading the territory of a sovereign nation – Iraq. So far the Government has refused to disclose the full advice given by the Attorney-General on the legality of the invasion.

Unlike George Bush, who has never expressed concern about the legality, Tony Blair and Jack Straw have always made it clear that legality was a central concern and a pre-condition. In an interview in the New Statesman of 27 September, Jack Straw told John Kampfner: “You know and I know that in this building [the Foreign Office] we are sticklers for abiding by international law.” Kampfner smiled and Straw went on: “And so is the Prime Minister, if that is what you're implying.”

It is tempting to argue that this is all irrelevant now. Surely, arguments about legality are an academic sideline of interest only to pettifogging lawyers. We got rid of Saddam, that's what matters. We have to deal with what is happening now, not what led up to it. But the problem is that we cannot hope for a better world without respect for law, and we certainly cannot export democracy, which depends on the rule of law, if we flout it ourselves. The invasion of Iraq is a precedent. If it is a bad one in law it must be exposed as such, lest it be used to justify future illegal attacks.

The great majority of international lawyers believe the war was illegal, as do Kofi Annan and his advisers. The minority is limited practically to one strand of opinion within the Foreign and Commonwealth office (but the deputy legal adviser, Elisabeth Wilmshurst, told the Butler Committee that she resigned because she disagreed with it), Professor Christopher Greenwood, who advised the Attorney-General, and the Attorney-General, Lord Goldsmith, himself.

On 17 March last year the Attorney-General summarised his views in a written answer to a question in the House of Lords. On the same day Jack Straw sent a copy of Lord Goldsmith's answer, accompanied by a longer memorandum from the Foreign and Commonwealth Office (FCO), to Donald Anderson MP, the chairman of the Foreign Affairs Select Committee. The legal background is the UN Charter, which says in Article 2 (4) that “all members shall refrain in their international relations from the threat or use of force against the territorial integrity or political independence of any state”. The only exceptions are where, as a last resort, collective action is authorised by the Security Council; and where a country exercises the “inherent right to individual or collective self-defence if an armed attack occurs against a Member of the United Nations”. All the lawyers accept that self-defence did not apply; hence the only legal justification could be in the form of Security Council authority.

The argument of the Attorney-General is that the authority exists from the combined effect of three Security Council resolutions: 678, 687 and 1441. The first of these in 1990 authorised Member States to use “all necessary means” (i.e. force) to eject Iraq from Kuwait and restore international peace and security in the area. This, of course, was achieved, and resolution 687 set out the conditions of the ceasefire, including the requirement for Iraq to get rid of any weapons of mass destruction. In resolution 1441 in 2002, the Security Council decided that Iraq had failed to disarm and was in material breach of the conditions laid down in resolution 678. Resolution 1441 did not itself authorise force and the Attorney-General does not dispute this.

In March 2003 the United States, supported by the United Kingdom, proposed a new resolution authorising force once again to disarm Iraq. However, the resolution was withdrawn when it became apparent to its proposers that it would be rejected. When the attack was launched without the proposed new resolution it could be justified only by claiming that no further resolution was needed after all, because the authorisation of force in resolution 678 remained valid 12 years later and was revived by Iraqi breaches of the later resolutions, even though a majority of the Security Council were known by the U.S. and Britain to oppose the new attack.

The media tried hard to investigate the legal authority for this claim. It failed to get beyond the Attorney-General's succinct written answer in the Lords. This was not and did not claim to be his full advice to the Cabinet or the Prime Minister. In October 2003 a Mr Evans wrote to the Cabinet Office, asking for complete copies of all the documents drawn up by the Attorney- General and giving the Prime Minister advice on military intervention in Iraq. Mr Evans based his application on the Code of Practice on Access to Government Information, which had been in operation since 1994. The Cabinet Office refused the request, relying on exemptions in the Code for “information whose disclosure would harm the frankness and candour of internal discussion” and “information covered by legal professional privilege”.

Refusal upheld

The courts had already been asked by the Campaign for Nuclear Disarmament (CND) to rule on the legality of the war before it started. CND asked for a declaration that an invasion based on resolution 1441 and without any further resolution would be in breach of international law. The Court of Appeal could have rejected the application on the basis that it is not their practice to give hypothetical judgments, but they recognised it was too important an issue to be dismissed so glibly. The judges were more impressed by the Government's argument that it would be contrary to the national interest to give a full statement of its legal position while international discussions were taking place. The FCO representative said, in the oblique language of his trade: “The UK's international alliances could be damaged by the incautious assertion of arguments under international law which affect the position of those other states. (It) could be of immense value to the potential adversary, allowing it to plan and adopt positions contrary to the interests of this country with greater assurance than would otherwise be the case.”

This hardly seems relevant considering the current situation in Iraq, and the only argument for continuing secrecy is the unworthy one that disclosure would discourage future government lawyers from giving frank and honest advice. I am sure Lord Goldsmith would not be influenced by that concern.

In its review of the intelligence on weapons of mass destruction, the Butler Committee of privy councillors had access in confidence to some, at least, of the Government legal advice which the public is being denied. They were able to give an account of how that advice was obtained and were told that on only three occasions in the last 100 years had the actual advice of the law officers to the Government been disclosed. In two cases – one of which was the Scott Inquiry – that advice was central to the issues in legal proceedings. The other arose from the Westland affair, when, after a leak of part of a letter from the Solicitor-General, the whole of the letter was published. Butler found that in the Iraq case the Attorney-General gave initial advice prior to resolution 1441. After that there was disagreement in the FCO on whether a further resolution was needed before the United Kingdom could lawfully use force. This led to Elizabeth Wilmshurst's resignation.

The Attorney-General told the Butler Committee he had a number of meetings about the legality issue with the Prime Minister, the Foreign Secretary, and other officials, including Sir Jeremy Greenstock, the UK Representative at the UN. He also met members of the U.S. administration. He then, on 7 March 2003, put his views in writing in a formal minute. Butler reveals, without quoting the text of the advice, that it required the Prime Minister in the absence of a further UN resolution to be satisfied that there were strong factual grounds for concluding that Iraq had failed to take the final opportunity to comply with its disarmament obligations under relevant resolutions of the Security Council. And that it was possible to demonstrate hard evidence of non-compliance and non-co-operation with the requirements of 1441, so as to justify the conclusion that Iraq was in further material breach of its obligations.

The Attorney-General gave his view of the legality of the invasion to the Cabinet by producing and speaking to the written answer he had given to Parliament. So we know that there were written opinions and a number of oral discussions when the Attorney-General gave his crucial advice which the Government persists in refusing to make public. Would we be any the wiser if this material were disclosed? Of course, the lurking suspicion is that the Attorney-General was much more equivocal than his written summary indicates, but there is no good reason to suppose that he ever changed his opinion or qualified it in ways which the published summary does not reveal.

In my own career in the law I have read many legal opinions and given a few myself. I have come to realise – as some lawyers seem unwilling to admit – that not every legal question has a “right” answer. This should not be surprising. Lawyers are supposed to know the law and how to apply it to the facts. Yet they frequently disagree. Cynics may say that is because it is in their interest to do so, but there are other explanations. Parliament (or the UN Security Council) may fail to spell out its intentions clearly enough; or the words of a statute do not clearly fit an unforeseen situation. Above all is the inescapable ambiguity of language itself.

Classic illustration

Resolution 678 was about liberating Kuwait, which was achieved in early 1991. The Attorney-General's argument is that this resolution was still in force or was revived 14 years later behind the back, as it were, of the Security Council. It hinges on the assertion that “international peace and security in the area” had, by virtue of the supposed failure of Iraq to comply with its disarmament obligations, not been restored. Although the predominant view of international lawyers is that resolution 678 became obsolete after the first Gulf war and was not revived, Lord Goldsmith's argument remains one that could be made in good faith.

Trading opinions gets us no nearer to a definitive answer. If everything that Lord Goldsmith has ever said on the subject is published, it would do no more than illustrate changes of mind or degrees of uncertainty before he reached his final view. It would not prove him right or wrong. We could get nearer to certainty by a ruling of a higher court. The International Criminal Court has jurisdiction over the actions of British troops, and the legality of the war could be relevant to a prosecution for war crimes, although a prosecution seems highly unlikely. A new Iraqi government might seek to bring the issue before the International Court of Justice at The Hague. Attempts to raise the issue in domestic courts, as in the CND case, have failed. The judges will strain every nerve to avoid what they see as political decisions. On this basis the courts rejected Lord Rees-Mogg's challenge to the Government's decision to embark on the first Gulf war.

There is no realistic prospect of an authoritative final ruling on the legality of the war. Tony Blair's desire to secure legal backing for the attack on Iraq was creditable and contrasts favourably with the contempt for law shown by President Bush. The backing Blair received was an implausible opinion, and not a ruling. What is already clear, without access to the full details of the Attorney-General's advice, is that the decision to go to war was based on a political judgment. Legality was a fig leaf.

We are left with an irony: the secondary importance of the legal advice surely undermines the case for continuing to conceal it? If and when the Information Commissioner in January demands that the full dossier be made public, it would be an intolerable abuse of power for the Government to use the veto which it has controversially maintained in the Freedom of Information Act. It will surely have the wisdom not to do so.