The name of Mohammed Meguerba featured constantly in the ricin trial at the Old Bailey, yet he appeared in neither the dock nor the witness box.

In the six months he spent in Britain in 2002, Meguerba was a key member of the poison plot. He was later to become the man who gave it away, after his arrest in Algeria late that year.

The first that the British police knew of the ricin plot came in the form of a 27-page memorandum written by Algerian intelligence agents who interrogated Meguerba in December 2002 and January 2003.

Now the 37-year-old terror suspect faces trial in Algeria over the London plot. He was deemed too risky a witness to be called before the Old Bailey. The Crown did not want him to appear because he might claim that he had been tortured in Algeria.

Defence teams too did not want him to appear at the Bourgass trial, fearing that his "confession" could prove devastating, because whatever questions surrounded the interrogation methods, the detail was frequently accurate.

Meguerba claims that he was recruited to the cause of jihad a decade ago when living in Dublin, where he arrived as an asylum seeker in 1995.

In April 1997 he married Sharon Gray, an Irish student, at Dublin Register Office. The marriage ended acrimoniously and Ms Gray won a non-molestation order against him. She has told police that his conversion to extremist Islam was a gradual process, beginning after he started to attend one of Dublin's small but growing number of mosques.

Meguerba told his interrogators he went to the mosque because he was lonely. In 2000 he fell into the company of a group of Islamist extremists.

Inspired by their ideas, he travelled via London to Pakistan and on to the Afghan terror camps where, according to the intelligence memo, he met Osama bin Laden on a number of occasions and was trained in the use of weapons and explosives.

He said he was tasked with carrying out attacks in Europe. He was able to supply police with details of the extensive European terror network run by Abu Doha, an Algerian terrorist currently in prison in London. He named several of the defendants acquitted of terror charges as members of the network.

Along with many trained terrorists, Meguerba was despatched to Europe just before the 9/11 atrocities to plan and execute attacks. At first he suffered a setback, when he was stopped at Schiphol airport, Amsterdam, in August 2001 in possession of a false passport. He was detained for four months. After being freed he resumed his journey travelling via France and Italy to arrive in the UK in March 2002.

Detectives believe it was his arrival that prompted Bourgass to put the poison plan into action.

Meguerba took on a senior role. His fingerprints were found on the original handwritten poison recipes and on items of equipment used for making the substances.

He claimed that two batches of ricin had actually been manufactured and were stored in Nivea pots - neither of them has yet been found.

He also helped organise the cell's finances, which came from credit card fraud and shoplifting. Meguerba was arrested in Norwich for credit card offences. Under the false name of Bruno Merillon, he was a director of Seven Roses, a company set up to run the east London market stall from which stolen clothing was sold.

Things went wrong in September 2002 when Meguerba was arrested in Tottenham, north London. He feigned a fit and was released on bail to return for questioning in December.

But the plotters feared that now that he was known to police, Meguerba might jeopardise the entire cell, and they urged him to flee London. He travelled to the gang's Manchester safe house, then flew from Liverpool airport to Barcelona.

From there he travelled to Morocco and was smuggled into into Algeria and to join a unit of the terrorist DHDS (Dhamat Houmet Daawa Salafia). His arrest led to the unravelling of the plot.

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