Transcripts of coded telephone calls to a Muslim cleric living in Madrid have provided the first proof of Usama bin Laden's hand in the September 11 attacks, according to Spanish police.

Sixteen days before the hijackings in America, an Al Qaeda agent telephoned the cleric in Madrid known as Abu Dahdah, boasting about the plot.

The agent, who calls himself  "Skakur," talks about how "in our lessons, we entered the field of aviation and we cut the bird’s throat."

Spanish police will say only that the call came from abroad on Aug. 27, but will not say whether it came from one of the hijackers.

Three weeks earlier "Shakur" had called to say: "I am preparing certain things which should please you." He gave a warning that his phone was "hot," which suggested that he realized that the conversation could be tapped.

Spanish police have not said why it took them until last week to arrest the cleric and seven others in Madrid and Granada who were charged at the weekend with helping to plan the Sept. 11 attacks.

They criticized Scotland Yard for not arresting another Muslim cleric, Abu Qatada.

Juan Cotino, the national police chief, said that he could not understand why the Jordanian-born scholar, living with his wife and six children in West London on housing benefit and who has been called Al Qaeda's "European ambassador," was still free.

Spanish police say that the burly figure of Abu Dahdah visited London at least 10 times, mostly they claim to visit Abu Qatada and other suspected bin Laden agents here.

Scotland Yard would not say whether they knew about these visits or if the Spanish authorities had made a formal request for them to detain Abu Qatada, who is alleged to have met a number of terrorist suspects at a community center in Baker Street.

Abu Qatada is alleged to be a member of Al Qaeda's fatwa committee, which provides Islamic authority for the group’s war on the West. He is believed to be among the MI5 list of suspects who would be jailed under the British government’s proposed emergency legislation. He was granted political asylum in 1993 after he was sentenced to life imprisonment in his absence by a Jordanian court for alleged involvement in a series of explosions.

When the Treasury froze his assets last month, they allegedly discovered $250,000 in a London bank account, which led to his benefits being stopped. He denies any links with bin Laden or any terrorist groups.

Investigators say that the bugged phone calls from Spain are a significant breakthrough in helping them to piece together how Al Qaeda's cells across Europe are linked.

The mystery figure making the calls talked of the air being "purer" than where they were, suggesting that the terrorists feared that they could be caught before carrying out their September mission.

For a man with four young children and not much money, 34-year-old Abu Dahdah was forever travelling abroad, with London his favourite destination. The bald, bespectacled cleric, who supposedly earned only $2,000 a month, used his Spanish passport to visit bin Laden twice in Afghanistan, one of his training camps in Indonesia as well as Sudan, Yemen, Turkey, Malaysia, the Philippines and various Gulf states.

One Spanish security source said: "Given he wasn’t going on holiday, we can only presume there are Al Qaeda links to all these places."

Police have admitted that they had Abu Dahdah and his group under surveillance for two years. Yet they did not monitor two meetings he is thought to have had in January and July in Spain with the leader of the hijackers, Mohammed Atta.

What has emerged from the Spanish investigation is how bin Laden also used the country as a holiday resort for some of his handpicked terrorists after missions abroad. Two of the hijackers are believed to have checked into a holiday hotel in Salou, near Barcelona, before flying to America to carry out their suicide mission.

Señor Cotino said that Abu Dahdah was also working closely with other Al Qaeda suspects in Belgium and Germany and that they, too, were still at large, much to the distress of his anti-terrorist investigators.

European police forces are being urged to work more closely together, but they are still reluctant to share all their intelligence and are bedevilled by rivalries.

Abu Dahdah and the seven other Islamic militants being held in Spain’s top security prison are accused of funding and helping to plan the September 11 outrage.

Detectives are investigating the part that they played in plotting bomb attacks in European cities.