Appealing for a new mechanism to be set up through the United Nations to be an arbiter of a more universal morality, Dr Williams said: “No government can simply be judge in its own case.”

Speaking in a lecture to the Royal Institute of International Affairs in London, Dr Williams made a detailed case against the use of the “just war” theory to justify the American and British case for going to war with Iraq.

Dr Williams said that the case for pre-emptive action could not be accommodated easily within the traditional Christian tradition. He said that America had lost the power of self-criticism and become trapped in a “self-referential morality”. It was fundamental to the just war theory that violence was not to be used by private individuals, he said.

“If a state or administration acts without due and visible attention to agreed international process, it acts in a way analogous to a private person. It purports to be judge of its own interest.”

Dr Williams said at his address at the remembrance service last week for the war in Iraq that Tony Blair and President Bush would be “called to account” for their decision to go to war. Last night he turned to the theory, formulated in the 13th century by Thomas Aquinas, who laid down that for a war to be just it must have the proper legal authority, the cause must be just and the intention good.

Dr Williams challenged the views of George Weigel, the Pope’s American biographer and a leading authority on the theory. Mr Weigel, senior Fellow of the Ethics and Public Policy Centre in Washington, delivered a lecture last October in which he defended a reading of the just war theory that would offer secure moral grounding for pre- emptive American action against Iraq. His works on the theory were circulated widely in the White House and many of those he worked with on the theory in the 1990s are now on Mr Bush’s staff.

Church leaders in England made clear in the run-up to the conflict that the Iraq war did not fulfil the criteria for a just war. The Bishop of Oxford, the Right Rev Richard Harries, the Church of England’s leading authority on the theory, said in August that the criteria had not been met and that Britain and America could not assure people that “will not unleash more evils than are already being endured”.

Dr Williams was one of a group of church leaders who told the Prime Minister in August that “an attack on Iraq would be both immoral and illegal”. Dr Williams, who remained silent during the conflict out of respect for the Armed Forces and others involved, said last night that he was not outlining an anti-American argument. “But, granting the weakness of international legal institutions and the practical difficulties entailed in activating them credibly, it is important to allow that no government can simply be judge in its own case in this respect,” he said.

“Indeed, this issue takes us back to one of the absolute fundamentals of just war theory: violence is not to be undertaken by private persons. If a state or administration acts without due and visible attention to agreed international process, it acts in a way analogous to a private person. It purports to be judge of its own interest.”

He argued that the present UN Security Council framework was inadequate and called for a standing commission on security within the UN that could advise and recommend UN intervention where necessary. Dr Williams said that at the centre of the just war theory was the principle that “that action which employs violence of some sort for the restoration of a broken or threatened social order does not have the nature of sin”.

He continued: “The private person must never use the violence that the ruler can rightly use, as they have the right of redress by due legal process.”

HOW THE JUST WAR THEORY EVOLVED

Modern thinking on what constitutes a just war has its roots in the writings of St Augustine and St Thomas Aquinas, whose rationales for war went largely unchallenged until the nuclear age and America’s disastrous experiment in Vietnam.

They stated that wars were just only if fought in a just cause, launched by a “right authority” — in practice, a sovereign state — and with righteous intentions.

Drawing on pagan as well as Christian traditions, St Augustine’s City of God, completed in the 5th century, set out the defence of a nation’s peace as the central justification for going to war. The crusades of the 11th, 12th and 13th centuries were backed by Augustinian just war thinking — their leaders claimed — not as wars of self-defence but wars to remedy the “great evil” of access to Christian holy sites being blocked by Muslims.

St Thomas Aquinas’s Summa Theologiae built on St Augustine’s writings, adding that no war should be waged without a reasonable chance of success and that once started, its means should be proportional to its ends.

Aquinas set out three conditions for a just war: auctoritas principis, justa causa and recta intentio.

It was used to justify the annihilation of the Ottomans at the Battle of Lepanto by the combined armies of Europe’s Catholic nations, Palmerston’s “forward policy” against imperial rivals in 19th-century central Asia and, implicitly, Britain’s declaration of war against Nazi Germany.

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