Kamel Bourgass, the presumed ringleader of an Islamic extremist group, was found guilty of conspiring to “commit a public nuisance by the use of poisons and/or explosives”.

Bourgass is already serving a life term after being convicted of murdering a policeman during a 2003 raid in Manchester.

Police raids on his London flat and other locations uncovered recipes and ingredients for making home-made poisons, instructions for explosives, as well as a CD-ROM in Arabic which “extolled the benefit of using bombs in furtherance of the Jihad”, or Islamic holy war.

The home-made poisons included ricin, a deadly toxin made from castor beans, and cyanide, botulism, nicotine poison and potato poison.

Police said the failed asylum-seeker had discussed various ways of spreading poison including smearing it on car door handles in London.

After the London raid on his flat in early January 2003, Bourgass fled to the city of Manchester, where he was cornered in an apartment by a police anti-terrorist unit.

In a failed attempt to flee, he fatally stabbed Detective Stephen Oake eight times with a kitchen knife and injured three other policemen.

He was given a life sentence, with minimum jail time of 22 years for the murder, and eight further years for wounding another officer.

In a major anti-terrorist operation, more than 100 others were arrested and 60 charged with criminal offences.

The operation mobilised 800 police officers and led to multiple investigations abroad including in Algeria, China, France, Spain, Switzerland and the United States.

The inquiry was launched in 2002 after a suspected terrorist awaiting trial in Algeria named Bourgass as an Al-Qaeda-trained terrorist who had already produced two pots of ricin.

Mohamed Merguerba’s testimony, taken in an Algerian jail in late December 2002, led to the raid eight days later on Bourgass’s London flat.

“This is an important conviction that has removed a very dangerous man from our streets,” said Metropolitan Police anti-terrorist chief Mr Peter Clarke.

“The public have been spared from a real and deadly threat.”

Four others on trial with Bourgass, all Algerian nationals, were acquitted of charges of conspiracy to murder and planning the attacks.

The trial results were published on Wednesday after the courts lifted a ban on media coverage that came into place shortly after Bourgass’s capture more than two years ago.

British authorities suspect Bourgass, thought to be between 28 and 32 and who used at least four false identities, received terrorist training at Al-Qaeda-run camps in Afghanistan.

He is believed to have been specially selected at the camps for instruction in making poisons and explosives.

Mr Clarke said Bourgass is also linked to Algeria’s Islamic extremist group GIA (Armed Islamic Group).

Britain’s home secretary Charles Clarke said the government would keep a “very close eye” on the men being freed.

He said the case had to “urge us on to find better ways of dealing with the (terrorist) threat”, citing identity cards, stricter immigration controls and a law passed last month which allows terrorism suspects to be put under limited house arrest.