The UK has made no decisions on backing a possible US attack on Iraq, Downing Street has insisted as it rejected claims the Navy was preparing for war.

Reports that aircraft carrier Ark Royal was being deployed to the Mediterranean so it could quickly move to the Gulf were branded "absolute rubbish" by Number 10.

We're taking part in very, very high profile and very high stakes sabre rattling

Patrick Mercer Conservative MP

The ship was taking part in an annual Nato exercise, which had been planned for the last 18 months or two years, said Tony Blair's spokesman.

That exercise came as Iraq invited the US Congress to send a team to Baghdad to search for evidence of weapons of mass destruction.

The prime minister is coming under increasing pressure to recall Parliament so MPs can debate possible military action against Iraq.

One of Labour's most senior backbench members, Tam Dalyell, has written to Mr Blair telling him he has a "moral obligation" to debate the issue.

But Number 10 repeated Mr Blair's assertion that he would not be pinned down on the specific way Parliament would be consulted about possible military action.

Fears that Iraqi President Saddam Hussein is building up weapons of mass destruction cannot be ignored, Mr Blair has argued.

His officials continue to insist the UK is not yet at the "point of decision making" over military strikes.

The Ark Royal is heading to the Mediterranean

Mr Dalyell said there was growing public concern that the United States would act without the backing of the United Nations (UN).

Mr Dalyell, the longest serving MP, has seized on a warning from former chief of defence staff Field Marshall Lord Bramall.

Lord Bramall has said the UK risks being swept into a very messy and long-lasting Middle East conflict.

Appeasing

He questioned whether US motivation was based on revenge after 11 September.

Mr Dalyell said those comments, and the views of 10 leading trade unionists who are urging the government not to support any US strikes, should persuade the prime minister to recall Parliament early in September.

US politicians are now openly debating the issues while the UK Parliament is being prevented from doing so, said the Linlithgow MP.

Fellow Labour MP David Winnick said Parliament should be recalled but argued most of his party colleagues would back action against Iraq.

Dalyell says Parliament is being prevented from debating Iraq

"With the greatest respect to Mr Dalyell, he is an appeaser of military and criminal dictatorships, which he has every right to be," said Mr Winnick.

"It is not because he approves of those regimes but because he will not accept military actions."

Listening to such critics is the past would have meant ethnic cleansing in Kosovo and crimes in Afghanistan would have continued, argued the MP.

A declaration signed by 2,500 church groups and religious leaders, including the next Archbishop of Canterbury Rowan Williams, is due to be handed into Downing Street on Tuesday.

Organised by Pax Christi it claims the US threats to attack Iraq without UN authority are deplorable and violate Christian moral teachings.

Training with US

The Ark Royal is to set sail for the Mediterranean next month.

With her aircraft and a state-of-the-art command centre installed on her in a recent refit, Ark Royal could play an important role in any attack on Iraq.

Conservative MP Patrick Mercer, a member of the Commons defence select committee, said war was not inevitable.

"But I think we're taking part in very, very high profile and very high stakes sabre rattling," Mr Mercer told Today.

Downing Street's strong denials of claims about war preparations stand in contrast to their reaction to reports about ships being prepared for action in Afghanistan last year.

Ark Royal will leave Portsmouth in five weeks time with a full complement of RAF and Navy Harrier jets, Merlin helicopters and 1,300 crew.

She will be accompanied by a Type 42 destroyer and may also be joined later by logistic landing ships and a contingent Royal Marines.

She will take part in two exercises, including an amphibious exercise with a US fleet in the central Mediterranean.