STARING confidently ahead as he arrives in Pakistan for what is believed to be a rendezvous with the mastermind who plotted the London attacks, one of the bombers, Mohammad Sidique Khan, hands his British passport to immigration officials.

Behind him in the queue of arrivals at Karachi airport is Shehzad Tanweer, 22, who told his family he was heading for a religious school.

Instead intelligence officials discovered the pair were picked up from the airport on November 19 last year and driven to a comfortable hotel in the business district of Karachi where they stayed for a week.

Immigration officials said that the third man from Leeds, Hasib Hussain, 18, had turned up in the same city five months before his colleagues.

Police toured hotels and restuarants with pictures of the men to discover who they met. Investigators are also trying to verify claims that all three slipped into Afghanistan during their trip to plan the attack on the London Underground.

Pakistani authorities have told The Times they know the identity of the British-born mastermind whom the British authorities are desperately trying to track down. “We believe this is where they could have met their mentor,” one Pakistani security source said. “They did not appear to go to where they told their families they were heading, and they have no obvious connection to Karachi, which was the centre of previous al-Qaeda operations.”

The trio avoided the tourist hotels in the city and settled for a three-star guesthouse in the Saddar commercial district, before moving on to Lahore and Faisalabad. Police want to know who paid their hotel bills.

One of the militants arrested by Pakistani police in connection with the London attacks is a suspected bomb-making expert for an outlawed terrorist group. Qari Usman, who has been linked to the plot to assassinate Pervez Musharraf, the Pakistani President, in 2003, is alleged to be part of the banned Jaish-e-Mohammad group. Some of its members were in contact with some of the British bombers this year. Mr Musharraf condemned the London bombings as “UnIslamic” and admitted some religious schools had terrorist links.

Officials in both countries are checking money transfers from Pakistan to Leeds and why all three men took circuituous routes to reach Pakistan. Hussain, 18, arrived from Riyadh on a Saudi Airlines flight SV714 on July 15, 2005. The other two first went via Istanbul on the same Turkish Airlines flight 1056 on November 19.

British officials are checking the authenticity of the men’s British passports. Hussain’s documents give his place of birth as High Wycombe, when his birth certificate states Leeds General Hospital. The fourth bomber, Jermaine Lindsay, lived close to High Wycombe. He too visited Pakistan and is also believed to have crossed into Afghanistan.

Khan, 30, is believed to have used the same British passport to visit Israel in February 2003. He stayed only for a day but Israeli officials are investigating whether he was on a reconaissance mission to plan a suicide attack in Tel Aviv by two Britons, also of Pakistani origin. In April 2003 three Israelis died in an explosion at a bar, Mike’s Place. Asif Hanif, from Hounslow in West London, blew himself up. The body of Omar Sharif was found floating in the sea a week later.

Tanweer and Khan met another British-born terror suspect, Zeeshan Siddiqui, during their time in Pakistan. As The Times revealed, Siddiqui’s best friend at a West London college was Asif Hanif.

British police in Islamabad were given permission to interview a key al-Qaeda figure, Mohammed Noor Khan, who was arrested in Pakistan last July, accused of sending messages for Osama bin Laden. His computer allegedly contained the names of overseas “sleeper cells” and details of landmarks and travel networks in Britain.

Scotland Yard detectives in Cairo are still questioning a Egyptian chemistry student at Leeds University, Magdi el-Nashar, about his alleged links with some of the bombers.

Police say they are puzzled why the terrorists left so much explosive and detonators in the hire car at Luton station and at their bomb factory in Leeds. The fear is that a second cell is at large but for some reason did not carry out their mission.

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