Tony Blair was warned before the Iraq war by the Attorney General, Lord Goldsmith, that a UN court could rule Britain's invasion unlawful, The Independent on Sunday has learnt.
The warning was in Lord Goldsmith's so far undisclosed legal opinion from 7 March last year, less than two weeks before the conflict began. Fearing that the International Court of Justice could rule it was illegal to go to war without the express authority of the UN Security Council, the Attorney General put senior barristers and international legal experts on standby to help to prepare the Government's defence if needed, legal sources said.
As Mr Blair prepares for Tuesday's parliamentary debate on the Butler inquiry, the revelation will intensify pressure on him to publish all Lord Goldsmith's legal advice leading up to the war.
Michael Howard, the Tory leader, is expected to join the chorus of those saying that John Scarlett, the chairman of the Joint Intelligence Committee, should be denied promotion to the job of the next head of MI6. But the Conservatives plan to concentrate their fire on Tony Blair.
Today, Mr Howard even suggested that if he had known then what the Butler report has since revealed about the preparations for war, he might have led his band of Tory MPs to vote against it. Interviewed by The Sunday Times he said: "It is difficult for someone, knowing everything that we know now, to have voted for that resolution."
Senior international legal experts have accused the Government of invading Iraq illegally, because it failed to get Security Council authority and there was no immediate threat to UK security. The former Foreign Secretary Sir Malcolm Rifkind, a QC, said: "I think there's a case to answer. I think it's hugely difficult to argue that when the Security Council refuses to pass a resolution you can simply unilaterally use a previous resolution as a case for going to war."
Charles Kennedy, the Lib Dem leader, will press Mr Blair on why the Hutton inquiry was not told that intelligence on Iraq's chemical and biological weapons had been withdrawn by M16 prior to the decision to go to war, because it was unreliable.
An indication of the strength of public feeling came from the Leicester South by-election last week. The Lib Dems won what was previously a safe Labour seat, and a candidate for the anti-war fringe group Respect took more than 3,700 votes.
The Butler report's revelations about the discrediting of WMD intelligence have been seized upon by international legal experts, led by Professor Philippe Sands of University College, London. The report also showed for the first time that Mr Blair had ignored the fact that UN inspectors could find no evidence of an active weapons programme in Iraq - despite legal advice that "incontrovertible" evidence was needed before an invasion.
The Government insists that the Attorney General is bound by rules of lawyer-client confidentiality, and that publication would undermine his freedom to give frank opinions to ministers. However, the barrister Michael Mansfield said civil service rules clearly allowed ministers to publish legal advice.
Sir Menzies Campbell QC, Lib Dem foreign affairs spokesman, said Lord Goldsmith's opinions went "to the very heart of the decision to take military action. The rule that the Attorney General's advice should not be published was conceived in the public interest. On this issue, the public interest in disclosure over-rides any other consideration".