Alleged links between Farid Hilali and the two biggest al-Qaeda attacks in the West make him one of the most important Islamist terrorist suspects held by Scotland Yard.

His arrest on Monday made him the first high-profile suspect detained in Britain under new European warrants designed to improve crossborder co-operation.

Mr Hilali, 35, from Morocco, is believed to be the shadowy figure, previously known as “Shakur”, who telephoned the alleged chief of al-Qaeda’s Madrid cell shortly before the September 11 attacks.

In a tapped call on August 27, 2001, Mr Hilali allegedly said that he “had entered into the field of aviation” and “cut the throat of the eagle”. Mr Hilali is also said to have promised that he would have something to show the Spain-based terrorist leader in about a month. The calls are reported to have been made from the New Cross or Peckham areas of southeast London.

Voice analysis and detective work led police to believe that Shakur and Mr Hilali were the same person.

The name “Shakur” appeared alongside Osama bin Laden and 33 others on an indictment in Spain last September for allegedly using the country as a base to plot September 11.

Mr Hilali was arrested by the Metropolitan Police last September. He was not charged but was discovered to be an illegal entrant and detained at Belmarsh prison.

He immediately claimed political asylum but his case has yet to be processed. Well-placed sources yesterday expressed doubt about any direct involvement in September 11 but suggested that his arrest was a significant development in the war against terrorism.

Baltasar Garzón, the judge leading the Spanish investigation, said last autumn that he had been unable to establish Shakur’s identity. But in April he made a new order saying that police had identified him as Mr Hilali, and calling for his extradition.

The Metropolitan Police formally arrested Mr Hilali on Monday and brought him before Bow Street Magistrates’ Court, accused of “participation in a terrorist organisation”. He was sent back to Belmarsh for seven days. The fast-track extradition procedure, introduced on January 1, should take three months.

The identity of Shakur has been a mystery since Judge Garzón first alleged that a Madrid terrorist cell prepared the September 11 attacks.

There is an alleged link between September 11 and the Madrid al-Qaeda cell blamed for the train bombings which killed 191 people in March.

Judge Garzón alleges that the 9/11 plot was finalised in 2001 at a meeting between Mohammed Atta, the leading hijacker, and Ramzi Binalshibh, a suspected al-Qaeda leader. One train bomb suspect has been charged with helping to arrange the meeting.

• The wife and brother of Lotfi Raissi, the Algerian pilot falsely accused of training the September 11 hijackers, has launched a £100,000 legal action against the Metropolitan Police for wrongful arrest.

  Sonia Raissi and Mohammed Raissi were arrested in September 2001. They allege that they were ordered to strip in front of officers and repeatedly questioned before being released without charge. Lotfi Raissi, 30, was held for almost six months on an extradition warrant from the US before being freed by a judge.

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