The Attorney General, Lord Goldsmith, changed his advice in the run-up to war in Iraq to declare that the conflict was legal, The Independent on Sunday has learnt.
Lord Goldsmith's full opinion on the legality of the war has never been made public. The desire to keep it secret is believed to be the main reason why the Official Secrets Act prosecution of Katharine Gun, a 29-year-old former employee of GCHQ, the Government's monitoring centre, was abandoned at the Old Bailey last week.
The case could have revealed that in November 2002 the Attorney General believed Britain required specific authorisation for war from the UN Security Council, but that he later changed his stance.
Ms Gun admitted leaking an email from the National Security Agency, the US equivalent of GCHQ, which called for British help in spying on diplomats at the United Nations in January last year. At the time, the US and Britain were seeking a Security Council resolution, later abandoned, specifically authorising the use of force against Iraq.
Although Ms Gun acknowledged she had broken the Official Secrets Act, her lawyers were preparing to argue that she had acted to prevent British casualties in an illegal war, and to demand that the Attorney General's full opinion be made public. An "advance notice of defence statement" filed in court highlighted differences in the Government over the legality of committing British troops without a UN resolution.
Elizabeth Wilmshurst, a deputy legal adviser to the Foreign Office, resigned on the eve of war in protest at Lord Goldsmith's opinion that the resolution was unnecessary. "Some agreed with the legal advice of the Attorney General," she said later. "I did not."
But the IoS has learnt from sources connected to the Gun case that in November 2002, when the Security Council passed resolution 1441, threatening "serious consequences" if Iraq did not "comply with its disarmament obligations", Lord Goldsmith agreed with the Foreign Office view that a further resolution would be needed to make war legal. As the possibility of war without such a resolution loomed, Britain's military chiefs of staff argued that they needed a clearer legal basis on which to proceed.
Between November and the end of January 2003, the IoS was told, the Attorney General's staff produced a paper dealing with the issues raised by the military chiefs, but it fell short of the legal authorisation the chiefs of staff wanted. "The military said they needed something harder if they were to commit troops," a legal source said. Lord Goldsmith's advice argued that a UN resolution from 13 years ago remained in force.
Clare Short, the former International Development Secretary whose UN spying claims caused a sensation last week, said even the Cabinet had not been allowed to see the full advice, but it is believed that Ms Gun's defence team was aware of its contents. Lord Goldsmith later said the decision to drop the case had been taken before the document was filed.
The Government continued to insist yesterday that it would not publish the Attorney General's full advice. But further court cases are pending in which lawyers are expected to mount a similar defence to Ms Gun's, and prosecution may be hampered if the advice remains secret.
Fourteen Greenpeace supporters face trial for a demonstration at a Southampton military base in February 2003, and five peace activists are charged with criminal damage at RAF Fairford. In all cases, the defence is expected to argue that, like Ms Gun, they were acting out of "necessity", to prevent an illegal war.