Laboratory did not reveal absence of ricin in plot cited by Blair

Tests demonstrating that no ricin was found at a flat linked to a gang suspected of planning a poison attack on the London Underground in January 2003 were not disclosed to police and ministers by officials at Porton Down.

The case, in which the suspects were later cleared, was cited by the Prime Minister and Colin Powell, the US Secretary of State, in the weeks leading up to the decision to go to war with Iraq.

A spokeswoman for the Defence Science and Technological Laboratory (DSTL), where the tests were done, said yesterday that officials at the establishment knew the results of the final tests three weeks after police had raided the flat in Wood Green, north London, on 5 January 2003. But she said that because of a "breakdown in communication" this information was not passed to the police for another 51 days.

On 3 February 2003 Tony Blair told the House of Commons that the "ricin terror plot" was "powerful evidence of the continuing terrorist threat". Two days later Colin Powell used the ricin evidence in a speech to the UN Security Council in which he warned of the danger of terror cells spreading from Iraq to Britain.

In April this year eight men, all immigrants, were cleared of involvement in the alleged ricin plot. Four were tried and found not guilty and a further four were acquitted after the prosecution offered no evidence against them.

Kamel Bourgass, 31, was found guilty of conspiring to cause a public nuisance through the use of poisons and explosives. He was also convicted in June last year of the murder of Detective Constable Stephen Oake, who was stabbed to death in Manchester in 2003 as Bourgass tried to escape. He was jailed for life.

But yesterday Charles Clarke ordered the arrest and deportation of seven men, including some of those cleared of the plot, hours before unveiling new plans to hold terror suspects without charge for up to three months.

Human rights group said the men must now be given a chance to challenge the grounds for deportation.

Gareth Peirce, solicitor for the men, accused the Government of abandoning the rule of law. She said all the men were innocent and had been properly cleared by a British court. She said they faced torture if they were sent back to Algeria.

She added: "[This Government's] actions make a mockery of jury trials and verdicts, of judicial decisions and of guarantees intended to be inalienable."

On 5 January 2003 an "indicative test" suggested that there were traces of the toxin at the flat in Wood Green. This information was given to journalists and made public the next day.

But after samples were taken to Porton Down in Wiltshire, the country's leading chemical weapons laboratory, it became clear, as early as 8 January, that the apparent traces were insufficient to be classed as ricin. Scientists received confirmation of this on 28 January, but police were not informed officially until 20 March - 51 days later.

DSTL, the Ministry of Defence agency which runs the laboratory, said scientists thought anti-terror officers had been briefed about the negative results. She said it was several weeks before they realised detectives had not been informed.

Michael Moore, defence spokesman for the Liberal Democrats, called for the Defence Select Committee to investigate the delay. "It is staggering that such a crucial piece of information did not get to the proper authorities, not least when it became so central to the political justification for the war in Iraq," he said.