Hassan Dabou has told of meetings at which Osama bin Laden vented his fury at al-Qaeda’s failure to demolish the World Trade Centre in 1993 and proclaimed his desire for revenge.

Mr Dabou was not sure what the target was to be, only that it would be a “large-scale operation in New York in the summer or autumn of 2001”.

Secret service chiefs are said to have taken seriously the tip from one of its veteran informants and immediately passed on the details to Washington.

While the agents were not sure what bin Laden was planning, they knew from Mr Dabou’s reports that al-Qaeda had sympathisers in place in several Moroccan cities.

Mr Dabou, who claims to have first worked as an informer for the secret service in the slums of Casablanca, was posted to Algeria and Iran. He says that he infiltrated the terror group after his employers sent him to Afghanistan, where he posed as an Islamic radical on the run from authorities in Morocco.

Reports from Casablanca say that Mr Dabou was flown in secret to Washington, where he was co-operating with US intelligence agents when the hijackers struck.

Growing evidence of al-Qaeda’s Moroccan links was not followed up by Western agencies last summer. Informers and minor figures arrested in Europe had revealed their associations with a number of Moroccans allied to radical Islamic groups, but the pattern was ignored.

Just 48 hours before the September 11 attack, the first link was established when Ahmed Shah Masood, leader of the Northern Alliance resistance to the Taleban in Afghanistan, was killed by a Moroccan and an accomplice.

In their frantic security sweeps since September 11, intelligence services in Britain, France, Italy, Spain and The Netherlands have arrested a large number of Moroccan nationals with alleged terrorist connections.

Morocco, being close to Europe, was an ideal base for bin Laden. His agents could move around the moderate Islamic country easily and use well-established smuggling routes into Spain.

Bin Laden’s agents are thought to have been in place in Moroccan cities for several years. The three Saudis being held as part of an alleged suicide bomb plot on American and British warships were all working in Casablanca and Rabat and two had followed the al-Qaeda instruction to marry local women. Al-Qaeda also found in the slums of Casablanca plenty of willing local recruits, who were moved to Europe to await their instructions.

Some of the volunteers were simply used as couriers. Some would be involved in counterfeiting credit cards and other scams to raise money, while a few were picked for terrorist operations.

Among them was said to be Zacharias Moussaoui, the former South London university student accused of being the would-be twentieth hijacker. He was born and raised in Morocco before moving to France and then Brixton.

Another volunteer was said to be Djamel Ajouaou, who was among the first group of eight suspected Islamic militants rounded up by British police last December and jailed in Belmarsh top-security prison under emergency laws introduced by David Blunkett, the Home Secretary. No reason was ever given for their arrest. Western security agencies were stunned when Mr Blunkett agreed that Mr Ajouaou could be sent to Morocco in January this year, even though his alleged terrorist links were detailed in court.

During a bail hearing, the former London hotel worker, who had lived in Britain for ten years, was described by Ian Burnett, QC, counsel for the Home Secretary, as “an active supporter of various international terrorist groups, including those directly engaged in terrorism and those with links to Osama bin Laden”. Protesting his innocence, Mr Ajouaouo was flown out of London in secret and was not allowed to take his British wife and four-month-old daughter with him.

One of the Britons being held at Camp X-Ray in Cuba, Tarek Dergoul, 24, a former East London care worker, is the son of a Moroccan baker. When Spanish police broke up an al-Qaeda cell, known as the “Soldiers of Allah”, they discovered that one of the ringleaders was a 35-year-old Moroccan, Najib Chaib Mohammed.

Two more of the suspects imprisoned at Camp X-Ray — Hamed Abderrahman Ahmed, 27, and Reswad Abdulsam, 30 — are Moroccans who were living in Spain before they went to Afghanistan. A gang of four Moroccans were arrested in Rome in February this year for allegedly trying to poison the water supply in the area near the US Embassy.

Another Moroccan, L’Houssaine Kherchtou, told a US court that he was sent on flying lessons in Kenya by al-Qaeda.

He became bin Laden’s personal pilot, but was puzzled when the al-Qaeda leader insisted that he learn to fly crop-dusters. US Intelligence believes the group was planning to use crop dusters for chemical attacks, with Kherchtou as one of the pilots.