The Times has learnt that American and British intelligence services have dismissed President Saddam Hussein’s 12,000-page declaration on Iraq’s weapons of mass destruction to be full of holes “big enough to drive a tank through”.

A Foreign Office official said that up-to-date information that appeared in the British intelligence dossier published in September is not mentioned in the Iraqi declaration.

Until now, the Government has been reluctant to give details of Britain’s likely involvement in a war with Iraq. Tony Blair has deliberately left the Americans to make all the running with their build-up of forces in the Gulf region, saying only that Britain was ready to play a “substantial” role.

According to authoritative sources, the Prime Minister wanted to ensure that the UN had a free rein to exploit all diplomatic efforts and to give weapons inspectors a reasonable period to do their work.

But with time running out for Britain to put its Armed Forces on war alert, the Government has been under pressure from the Service chiefs to allow deployments to begin. The Government is expected to make an announcement before Christmas in the first concrete sign that Britain is ready to join the Americans in fighting a second war against Iraq.

The Government is likely to indicate its general plan for troop movements soon after the UN Security Council meeting next Thursday at which Saddam’s weapons declaration will be discussed.

Officials in Washington said that America would keep its views on the declaration to itself until it had talked to the inspectors at that Security Council meeting. Ari Fleischer, White House spokesman, said: “We will continue to be deliberative and thoughtful as we review this document.”

Washington has insisted that the dossier itself would not necessarily be a trigger for war, although UN diplomats expect President Bush to say that the omissions in the Iraqi declaration amount to a “material breach” of the UN resolution, which obliged Baghdad to deliver a complete and current list of its arsenal.

The problem for the British military is that their American counterparts view the ideal time for an attack on Iraq as between now and April.

The Americans are so far advanced with their build-up, both in the Gulf and at the key B2 and B52 bomber base at Diego Garcia in the Indian Ocean, that they could be ready for war at comparatively short notice. There are still four US aircraft carriers in the vicinity, although at least one, USS George Washington, is now on her way home, having been relieved by USS Harry S. Truman.

By contrast Britain, which has not officially sent any troops to the region to prepare for war, will need several weeks to deploy and acclimatise. Under current contingencies, troops earmarked for Iraq are likely to be allowed to spend Christmas at home with their families before beginning the move to the Gulf.

British troops from 7th Armoured Brigade and 4th Armoured Brigade in Germany, part of the 1st (UK) Armoured Division, are training at their bases for what is expected to be the main British land force.

Other key elements will also be ready early in the new year, including the aircraft carrier HMS Ark Royal, which is due to leave Portsmouth towards the end of next month for a Naval Task Group training deployment in the Far East. HMS Ocean, the helicopter and Royal Marine Commando carrier, will also be ready for operational service in a few weeks.

For the Government, the Saddam dossier has made it easier to go public about British military plans. British officials who have seen the document say that many biological and chemical warfare materials and missiles that escaped previous UN weapons inspections in the 1990s were still unaccounted for. They are not mentioned in the Saddam declaration. “We know they have been hidden,” one official said.

US officials confirmed to The Times that the Administration’s initial assessment was that the declaration mainly comprised previously published statements. The US had expected this and was looking for a “pattern of abuses”.

Mr Bush said last night that it was too early to tell whether Saddam was lying. But he added: “I don’t want to prejudge the report. But my gut feeling about Saddam Hussein is that he is a man who deceives, denies.”

Additional reporting by Elaine Monaghan in Washington and James Bone in New York

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