Politics - John Kampfner finds ministers with legal worries

Ministers are worried about a court case that challenges the lawfulness of military action in Iraq.

Tony Blair began the case for his defence a week early. His belated but still incomplete admission that weapons of mass destruction will not be found will be superseded by the findings of Lord Butler on 14 July. The focus will return, Downing Street hopes only briefly, to the use of intelligence on the road to war. But niggling away is also the question of the legal status of the decision to invade Iraq.

In this difficult fortnight, the Prime Minister's fate rests on the willingness of the five-strong Butler team to judge the veracity - as well as the accuracy - of the government's apocalyptic assertions on WMDs. If they accept Blair's version of events, that he believed the intelligence to be correct at the time of delivering his dossier of September 2002, and when making his subsequent statements, then the damage will be containable. If the criticisms are confined to institutions, to a breaking of the "Chinese walls" between No 10 and the Joint Intelligence Committee, then he will accept the findings, admit mistakes, promise changes, and hope to move on. Contrition will not extend to the decision to go to war.

Butler may be reluctant, I am told, to offer a judgement on the legal opinion provided by Lord Goldsmith on the eve of war. To do so would technically stray beyond his remit. The Butler review has spent considerable time looking at intelligence on WMDs in countries such as North Korea and Iran, beyond Iraq. The only area in its terms of reference that allows any scope for political conclusions is the line which asks the committee "to examine any discrepancies between the intelligence gathered, evaluated and used by the government before the conflict, and between that intelligence and what has been discovered by the Iraq Survey Group since the end of the conflict". The word used (my italics) is the tough one.

Butler has heard from the main players involved in the legal case, among them Elizabeth Wilmshurst, who resigned as the Foreign Office's deputy legal adviser in protest days before the war, Sir Jeremy Greenstock, mainly for his role as UK ambassador to the United Nations, and Goldsmith himself. They have provided differing interpretations. Goldsmith's legal opinion, and the story of how he was prevailed upon at the last minute to change his mind, continues to haunt him, according to legal figures. It helps explain his recent condemnation of the detention of four Britons at Guantanamo Bay when he spoke of "no compromise" on certain principles and argued that the US tribunals would not offer a fair trial. When he appeared before the Commons liaison committee on 6 July, Blair talked of the camp being an "anomaly" - but expressed sympathy with the Bush administration.

Inside Whitehall, unease at the precariousness of the legal case for war remains strong. Little noticed outside government and legal circles, the prosecution of five peace activists charged with trying to disrupt US B-52 bombers taking off from RAF Fairford in March 2003 is causing considerable concern. It is now before the Court of Appeal, the furthest any trial based on a ministerial decision to take military action has ever reached. It is being seen as a test case. On 29 June, ten minutes before the hearing was due to begin, Sir Michael Jay, permanent under-secretary at the Foreign Office, handed in a submission seeking to reinforce the government's position that British courts have no jurisdiction to rule on the lawfulness of military action.

Jay's five-page paper, delivered on behalf of Jack Straw, the Foreign Secretary, argued that any opinion delivered by a court "would be prejudicial to the national interest and to the conduct of the government's foreign policy". It would, he said, have a detrimental effect on British diplomacy and would "risk weakening the international consensus" in support of the new Iraqi government led by Iyad Allawi; it would also "undermine the UK government's standing in its relations with Arab and Islamic countries and could give comfort and encouragement to terrorist organisations".

The case arises from a High Court ruling in May that said the defendants could not raise the legality of the war itself - in effect, that "Crown prerogative" provides governments with immunity for executive decisions - but that they could mount the defence of "necessity" to prevent death or injury.

The crime being cited by defence lawyers is the same as was used by the allies at the Nuremberg trials - "crime against peace".

Lurking not far behind, though not applicable in this case, is the International Criminal Court in The Hague. It has so far codified "war crimes" - the charge on which Slobodan Milosevic is currently standing trial - but it has yet to codify "crimes of aggression", such as those invasions that have not explicitly been endorsed by the UN. The government is anxiously watching.