Britain's near-total support for the United States' policy in Iraq is about to break down over the question of whether Saddam Hussein and other senior members of the Baath party should face execution.
Last week, the Foreign Office slipped out a warning that the UK will boycott the upcoming trial of Saddam if there is any risk of the former dictator being put to death.
The Government's legal advisers are also grappling with the intractable legal dilemma of what to do with former high-ranking officials now held in British-run jails.
This is one of many unresolved problems about the handover to an Iraqi administration which is causing friction between London and Washington. In private, Foreign Office officials have been driven to despair by the failure of the Americans to plan for the 30 June handover.
Their fears were voiced yesterday by Sir Christopher Meyer, a former ambassador to Washington. He told BBC Radio 4's The Week in Westminster: "Having not been able ... to get our views into the administration ... on how you handled Iraq after Saddam Hussein, we need to be ... certain that that doesn't happen now when we come to this crucial date of 30 June.
"The President intends in a week's time to come out with a detailed plan about how the handover of sovereignty will be made: all I can say is that I hope... it takes into account the views of the British Government."
Sir Malcolm Rifkind, a former foreign secretary, echoes diplomats' frustration in an article in today's Independent on Sunday in which he calls for responsibility for Iraq to be taken away from Donald Rumsfeld, US Defence Secretary, and the Pentagon and handed to the State Department, headed by Colin Powell.
Government policy and the European Convention on Human Rights lay down that the British cannot hand the prisoners over if there is any risk of them being executed. The death penalty has been suspended in Iraq, on British insistence, but is expected to be reintroduced.
The problem is so sensitive that the Foreign Office is refusing to say which former Baath leaders are now in British-run jails, or what they are accused of.
Human rights groups in Britain have been trying to establish who they are so that they can obtain a court order preventing the British authorities from handing them over, unless the new Iraqi government undertakes not to bring back the death penalty.
A Foreign Office official said: "The imposition of the death penalty is a matter for sovereign states, and the UK has to maintain relations with 'retentionist' states, including for example the United States and China. We cannot treat Iraq any differently.
"It would be prejudicial to specify who may face prosecution before the tribunal, but as in all other circumstance, we would seek assurances that anyone passed to another jurisdiction would not face the death penalty. We're not in that position yet."
Kate Allen, UK director of Amnesty International, said: "The death penalty is arbitrary, cruel and wrong... The UK authorities must obtain assurances that prisoners will not face the death penalty before handing them over to another authority."
The Iraqi Governing Council has already passed a decree which means that officials of the old regime will face trial by a special tribunal. Saddam Hussein will be handed over by his American captors, who have no compunction about seeing him executed.
Bill Rammell, a Foreign Office minister, said last week, in a written answer to a question from the Tory MP Andrew Robathan, who wants the death penalty re-introduced in the UK, that the British authorities will have to refuse to supply any evidence that might help send the former president to his death. But Mr Rammell also hinted that the Iraqis will have little trouble finding evidence to execute Saddam without British co-operation.