The British Government is being pressed to publish the full legal advice it received from Attorney-General Lord Goldsmith on the legality of war against Iraq. A summary of his advice that the war was legal was published on 17 March 2003, just before the war started.
BBC News Online world affairs correspondent Paul Reynolds looks at some of the key questions on this issue.
Why is the government not publishing the full advice?
Because it says that this would break the convention that legal advice to the government is not published. This is seen as similar to the principle that detailed legal advice to ordinary citizens is normally confidential.
Lord Goldsmith: A summary of his advice was published before the war
Lord Goldsmith himself told the House of Lords: "There is a long standing convention adhered to by successive governments that legal advice from the Law Officers is not publicly disclosed."
He quoted from the Ministerial Code which guides the actions of British ministers. This states in paragraph 24: "The fact and content of opinions or advice given by the Law Officers...must not be disclosed outside Government without their authority."
Paragraph 23 says that if the Cabinet is given a summary, it should also be given the full version. According to former Cabinet minister Clare Short this did not happen.
If the advice is already published in summary, why not in full?
This is a point made by critics of the government who argue that it is inconsistent to publish the summary but not the full argument. The government certainly could do so.
The Ministerial Code says that the "authority" of the Law Officers is required before their opinion can be published but not that it cannot be published.
The decision to publish the Iraq summary was a compromise. The government argued that, in this way, the advice was made known but that some confidentiality was preserved.
The government argument is that such disclosures should be kept to an absolute minimum. Otherwise, there would be demands for such publication across the range of policies.
Would the full argument differ from the summary statement?
Lord Goldsmith says not. He told the House of Lords: "The statement was ...consistent with my detailed legal advice."
However, getting access to the detailed advice would enable critics to argue the case more closely and to see if there were weaknesses in the arguments behind the advice.
Critics also want to know when the opinion was finally arrived at and whether it changed during the run-up to war.
Protesters in one court case want to know whether, at the time of their alleged offences, the Attorney-General himself was wondering whether a specific Security Council Resolution authorising war would be necessary.
What was the case the Attorney-General made?
The Attorney-General argued that "authority to use force against Iraq exists from the combined effect" of three Security Council resolutions, all adopted under the section of the UN Charter "which allows the use of force for the express purpose of restoring international peace and security".
These were Resolutions 678, 687 and 1441. 678 goes back to November 1990. It authorised the use of force to remove Iraq from Kuwait and to restore peace and security in the area.
Resolution 687 (April 1991) laid down conditions for the ceasefire with Iraq after the Gulf War and Lord Goldsmith argued that it "suspended but did not terminate the authority to use force under Resolution 678".
Resolution 1441 (November 2002) said that Iraq had been in breach of 687 because it had not disarmed properly and that if it did not cooperate fully, a further material breach would occur.
Lord Goldsmith argued: "It is plain that Iraq has failed to comply and therefore Iraq ...continues to be in material breach."
He stated: "Thus, the authority to use force under Resolution 678 has revived and so continues today."
He further said that if a new resolution specifically authorising force had been required, 1441 would have made this clear.
What are the counter arguments?
The critics say that the Attorney-General relied too much on UN resolutions from too long ago and ignored the requirement that specific authorisation for war was needed.
Thus two lawyers for the Campaign for Nuclear Disarmament argued in March 2003: "First, resolution 1441 does not expressly authorise Member States to use force. The resolutions adopted by the Security Council over the years,
including Resolution 678, show that that the language used to authorise force is bold and consistent.
"Member states are 'authorised' to 'use all necessary means' or 'take all necessary measures' in pursuit of a
specified goal. These words are manifestly absent from Resolution 1441."
They also argued that "as a matter of principle, international law precludes Member States from relying on any implied authorisation to use force. The prohibition on the use of force contained in Article 2(4) of the UN
Charter is one of the most fundamental principles in the Charter".
"Member States may only derogate from that prohibition in self-defence or following an authorisation from the Security Council to use force made under Chapter VII of the Charter."
Do lawyers agree on this issue?
No. Even within the government, opinions differed. The deputy legal adviser at the Foreign Office, Elizabeth Wilmshurst, resigned.
She said later: "I left my job because I did not agree that the use of force against Iraq was lawful and in all the circumstances I did not want to continue as a legal adviser."
Was the war against Serbia in 1999 not conducted without UN approval?
Yes. The Nato powers decided not to ask for UN authorisation because they knew that Russia would veto a resolution. So they argued that there was a humanitarian crisis in Kosovo which justified intervention.
Thus they developed a new concept in international law, that of intervention on humanitarian grounds even in the absence of a resolution authorising force. A feeling of guilt over the UN's failure to act in Rwanda helped bring about such thinking.
This argument was not the main one used in the case of Iraq, however.
Can the UN itself make a ruling on the legality of the war?
The UN's own court, the International Court of Justice, could be asked for an advisory opinion but only by a relevant UN body such as the Security Council or General Assembly. There is at present no sign of that happening.
International law is not like national law. Certain principles have been agreed but putting them into practice depends on agreed interpretation and the co-operation of governments. These are sometimes missing.