There were unsubstantiated reports that the Queen and the Prime Minister may have been involved in the exercise in a Downing Street bunker.
The disclosure by Whitehall officials underlined the seriousness with which the Government is reacting to risks of a terrorist attack from the Iraqi leader, Saddam Hussein, following the all-ports alert about a possible attempt to smuggle anthrax into Britain by using duty free spirits, or scent.
Jack Straw, the Home Secretary, also disclosed that a warning that President Saddam could be planning to flood the West with anthrax hidden in bottles disguised as duty-free goods was received 13 days before the Government alerted the ports.
In a further development, an Iraqi scientist who may have tipped off Western intelligence agencies about the anthrax threat and who was planning to defect is reported to have been arrested and thrown into prison.
MI5 alerted Customs and Excise officers and Special Branch police at British ports on a number of occasions this year following intelligence suggesting Iraq may be planning biological or chemical attacks.
While the most recent report told ports to be on the look-out for anthrax, information about other named substances has been released.
Iraq is known to have reserves of Agent VX, a highly toxic nerve agent used against the Kurds, mustard gas, which cause terrible skin damage, and sarin, the nerve agent used in Nazi gas chambers, aflatoxin, which destroys the immune system, and botulinum toxin.
A security source said the anthrax alert was "one of a number of warnings about the possible threat from Iraqi biological and chemical weapons" that had been issued to the authorities guarding ports and airports, including the Channel tunnel and Eurostar.
The source stressed that there was no intelligence to suggest that Britain was to be specifically targeted. The anthrax alert said the threat was against "the enemies of Iraq".
Meanwhile, an official with Unscom, the United Nations body charged with rooting out Iraq's clandestine weapons programmes, confirmed yesterday that it was informed of the arrest of Nassir al-Hindawi by the Iraqi government earlier this month.
According to Baghdad, Mr Hindawi was found to be preparing his own flight from Iraq and had important documents about the biological weapons programme, which he intended handing over to Western investigators.
Mr Hindawi is considered to have been one of the key pioneers of Iraq's biological campaign. Anthrax would have been one of the agents Mr Hindawi would have been trying to put into production for Baghdad.
Ewen Buchanan, the Unscom spokesman, confirmed that Mr Hindawi has been interviewed repeatedly by Unscom investigators, though not recently.
Underplaying the importance of Mr Hindawi, Mr Buchanan said he "was not involved in the production phase" and added that Unscom has interviewed "hundreds of other people", besides Mr Hindawi.
Other experts, however, suggested that had he successfully defected, Mr Hindawi could have been crucial to Unscom's efforts to reveal the truth about Iraq's biological ambitions.
Confirmation yesterday by Mr Straw to the Commons that a number of "all- ports" alerts had been made since the tension in the Gulf, fuelled suspicions among Labour MPs opposed to war against Iraq that the latest reports are part of a conspiracy to wreck the peace deal brokered with Iraq by the UN Secretary-General, Kofi Annan.
"I am extremely suspicious that this is an attempt to destabilise the agreement over the ceasefire when it seems to be working rather well.
"It seems to be the action of somebody who wants to fight," said Tam Dalyell, the veteran Labour campaigner.