A former MI5 agent claimed last week that intelligence chiefs failed to act after he told them that about 20 members of a group with links to Bin Laden�s Al-Qaeda network were operating inside the mosque.

The informer said several of the men were engaged in a counterfeit credit card ring that raised tens of thousands of pounds to fund terrorist activities abroad. The cards were sold for £ 150 each to dozens of supporters of Abu Qatada, the cleric, who then used them to buy electrical goods, furniture and clothes.

The goods were then resold on the black market. Some of the profits went to buy communications equipment such as satellite telephones, computers and, it is believed, weapons in eastern Europe. The goods were then shipped to Islamic fighters in Algeria and Afghanistan.

A Spanish judge said last week that the leader of an Al-Qaeda cell in Madrid that had direct links to the September 11 attacks on the United States had visited Britain to make contact with the cleric.

Details of the warnings given to MI5 about Qatada, a Palestinian, have been disclosed for the first time by Reda Hassaine, who said he was paid to infiltrate the mosque in north London.

Hassaine said that in 1999 he was instructed by his MI5 handler to meet Qatada twice a month and infiltrate Bin Laden's network in London. The operation ended abruptly last year after one of Qatada's bodyguards became suspicious and beat up Hassaine.

Last week Hassaine said Qatada should have been detained by police. However, his MI5 handlers told him that, despite his dossier of allegations, there was 'no evidence' that Qatada had committed any crime in Britain and that it was not possible to deport him.

Whitehall sources have privately confirmed that Hassaine was involved in an intelligence-gathering operation against Qatada but declined to explain why they have not taken further action.

Qatada is wanted in Jordan after being convicted of masterminding and financing a series of bomb attacks against tourists to coincide with the millennium celebrations.

Hassaine said he described in a series of written reports to MI5 how Qatada was the 'spiritual leader' of a banned Algerian terror organisation called the Salafist Group for Call and Combat, known as GSPC. The group is said by security officials to be 'affiliated' to Bin Laden's Al-Qaeda network. It was banned when the Terrorism Act came into force in March this year.

Last February Qatada and seven other men, said to be members of the GSPC's British cell, were arrested in London after the discovery of plans to bomb or use sarin nerve gas against an unspecified target in Strasbourg. Charges against Qatada were not pursued.

During the investigation, codenamed Operation Odin, Special Branch officers raided Qatada's home, a run-down semi-detached house in Acton, west London, and found more than £100,000 in cash. Security sources have linked some of the money to collections held by Qatada at a local leisure centre, which doubled as his mosque until last year.

Hassaine said that Qatada, whose accounts have now been frozen, would stand on a wooden chair in front of his audience at the mosque and urge his followers to contribute to the Islamic holy war.

"He would hold out a plastic box and tell his supporters that it was their duty to give as much as they could to help the jihad. He told them that God would reimburse them. There might have been 200 people there and some would give up to  £50."

Hassaine recalled that when Qatada issued a fatwa, "he said that it was legitimate for fighters waging the holy war in Algeria and other Arab countries to kill the women and children of members of the security forces. He said the children had to be given the right to go to paradise".

Spanish investigators want to question Qatada over his links with at least seven Al-Qaeda activists being held in Spain over the September 11 attacks. MI5 monitored the group's leader, Abu Dahdah, on at least 20 occasions when he visited Qatada in Britain.

Qatada denies any links with Bin Laden but says that he fully expects to be arrested soon under new anti-terror laws.

"In this country you just wanted a target to shoot at and you wanted someone to talk about," he said. "I am a big target with a big belly."