Rumsfeld: US may have to launch war without Britain

America has suggested for the first time that Britain may have to reduce its role in a war against Iraq – or not take part at all – because of Tony Blair's political difficulties.

Asked whether the US would go to war without Britain or with Britain playing a smaller part than planned, Donald Rumsfeld, the US Defence Secretary, said Britain's situation was "distinctive", an apparent reference to the opposition among the public and Labour MPs to an invasion without the passage of a second United Nations resolution. Mr Blair faced fresh pressure yesterday when 40 Labour MPs called publicly for him to step aside.

Mr Rumsfeld said: "What will ultimately be decided is unclear as to their [Britain's] role in the event that a decision is made to use force." Speaking at the Pentagon, he added "Until we know what the resolution is, we won't know what their role will be and the extent they'll be able to participate."

Mr Rumsfeld said he had spoken to Geoff Hoon, his British counterpart, yesterday about plans for war. Britain has more than 25,000 troops in the Gulf, with a US force of more than 200,000.

Such was the consternation caused in Whitehall by the remarks, that Mr Rumsfeld's office later issued a written statement of clarification saying his main point had been that obtaining a second resolution "is important to the United Kingdom" and that both countries were working to achieve it.

"In the event that a decision to use force is made, we have every reason to believe there will be a significant military contribution from the United Kingdom," his statement said.

British officials sought to play down the significance of Mr Rumsfeld's remarks, professing optimism that Britain and the US were on track to obtain the nine Security Council votes needed to secure at least a "moral majority", despite veto threats by France and Russia. Mr Blair's spokesman said Britain's focus remained on a second UN resolution, and stressed "there has been total co-operation in military planning between ourselves and the Americans".

However, Sir Christopher Meyer, the outgoing British Ambassador to Washington, suggested the US could go ahead without the UK. "I am pretty clear that they would go to war in whatever circumstance," he told Channel 4 News. The episode underscores the strains between Washington and London.

The Rumsfeld comments came as Mr Blair convened for the first time an embryonic "war cabinet" of ministers and military personnel.

As British and American diplomats scrambled to round up the required Security Council votes, the atmospheres in Downing Street and the White House were very different. The British desperation was evident in the search for a compromise to secure the Security Council majority the government believes will smooth the worst of the criticism. Mr Blair telephoned leaders of the "swing six" states. Last night, the six waverers had still not signed up to any form of words despite two key British concessions: an extension beyond 17 March of the deadline for Iraq to comply, and a check list of disarmament demands. The Security Council vote has now been delayed until tomorrow at the earliest.

In Washington, by contrast, the prevailing mood was of frustration at the delay. Ruling out the 45-day extension in the proposed 17 March deadline that had been pushed by undecided members of the Council, the White House said even a month's extension was a "non-starter".

The divergence is also plain in public opinion. In Britain, only 19 per cent of the public would back British participation in an attack on Iraq without a new UN resolution. In the US, however, 55 per cent would support an American invasion even in defiance of a vote at the Security Council, a New York Times/CBS News poll found.

Mr Blair's difficulties may have been intensified by Kofi Annan's remarks at The Hague on Monday. Mr Annan said that if there was no UN authorisation for military action, "the legitimacy and support of any such action will be seriously impaired".

A Foreign Office spokesman said: "We always act in accordance with international law." But officials took pains not to repeat their earlier view that UN resolution 1441 provided legal justification for war. Previously the British interpretation was that, while politically desirable, a second resolution was not necessary to legitimise military action. The new British silence about 1441 suggested that obtaining a second resolution might now be legally necessary.

Legal experts added to the doubts by saying British troops could be the first defendants to face war crimes charges if the government joined a war without UN backing. Even the accidental bombing of Iraqi civilian targets could trigger criminal prosecutions, senior lawyers warned last night.

In an escalation of the psychological pressure against President Saddam, the air force tested the biggest conventional bomb in the US arsenal, a 21,000lb munition that could play a dramatic role in an attack on Iraq.

The bomb is guided to its target by satellite signals. The detonation was expected to create a mushroom cloud visible for miles.