The NBC (nuclear, biological and chemical) suits were discovered during a raid by 150 police officers on the Finsbury Park mosque last Monday. Informed sources said the discovery confirmed growing fears by police and MI5 that a chemical attack is being planned by supporters of Osama Bin Laden’s Al-Qaeda movement in Britain.

Police announced after the raid they had seized a small arsenal of weapons including a stun gun, an imitation firearm and a CS gas canister.

But discovery of the NBC suits has been kept a closely guarded secret known only to a handful of senior officers. Ministers are acutely aware that any suggestion that the mosque may have been involved with chemical weapons could inflame racial tensions. Seven men — six north Africans and one eastern European — were arrested during the raid. Last night two were still being held under the terrorism act.

It is not known how many suits were found at the mosque or their purpose. However, police say there has so far been no evidence found of chemicals or anything that would pose an immediate threat to the public.

The suits are being analysed to see if there are any traces of ricin or other chemicals on them. Scientists at the defence science and technology laboratories at Porton Down are thought to have been consulted.

Police emphasised that the operation was not against the mosque itself or those who regularly attend it to pray.

Reda Husseine, an Algerian journalist once paid by French and British security services to infiltrate the mosque, said he had heard conversations by militants there about the possible use of chemical weapons. He said: “In 1999 and 2000, there were discussions about chemical, biological and even a possible attack with a ‘dirty bomb’ (a crudely constructed device containing uranium). I told British authorities about that. They dismissed it as rubbish.”

The mosque has been used by Abu Hamza, a radical Muslim cleric, to preach holy war against the West. Its visitors have included two would-be suicide bombers. One was Richard Reid, the “shoe bomber”, who tried to blow up a plane using plastic explosives in his shoe in December 2001. A second was Zacarias Moussaoui, the man the FBI claims was to be the 20th hijacker on September 11.

Scotland Yard has said the search of the mosque last week was linked to a raid earlier this month on a flat in Wood Green, north London, where ricin is believed to have been made. Four north Africans have been charged with being concerned in the development or production of chemical weapons.

Police mounted the operations after receiving information on New Year’s Day of a threatened chemical attack in Britain. Officers fear there may be chemical “factories” operating elsewhere in Britain.

Last month a chemical warfare suit was seized after French police arrested four suspects in a Paris suburb. Sources say that raid has helped investigators in Britain begin to unravel a new terrorist network.

A typical NBC suit consists of hooded overalls, protective boots and inner and outer gloves. A cloth outer suit impregnated with carbon and a respirator are designed to protect users from chemical, biological or nuclear fallout.

Scotland Yard said it was “not prepared to discuss” the investigation.

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