MAGDY EL-NASHAR, the Egyptian chemisty student who befriended some of the bombers in Leeds, was arrested by police in Cairo in a dawn raid yesterday. Scotland Yard detectives are expected to question him over the weekend.

However, Habib el-Adly, the Egyptian Interior Minister, was quoted in today’s edition of the pro-government daily newspaper al-Gomhouria as saying that “the Egyptian chemist Magdy el-Nashar has nothing to do with al-Qaeda.”

In Pakistan, intelligence agents arrested the head of an Islamic religious school last night where the suicide bomber Shehzad Tanweer is alleged to have first made contact with al-Qaeda figures. The head of the madrassa was among four men seized at the start of a crackdown ordered in Pakistan by President Musharraf after the London bombings.

Agents claim that Tanweer spent five days at a madrassa at Muridke, 20 miles north of Lahore, which is run by an outlawed terror group, although officials at the school deny this. It is not known if it is the leader of this campus that has been seized. Officials in Islamabad say that Britain has sent a list of names they want traced, most of them British-born.

Details of the network that recruited the British suicide bombers are emerging as police piece together the final months of Tanweer, the Aldgate Tube bomber. Pakistani officials have established that when Tanweer, 22, was supposed to be studying at a religious school he met a British-born militant, Zeeshan Siddiqui, who was arrested for terror offences.

Scotland Yard now wish to question Siddiqui, who stunned his parents in West London when he dropped out of college in 1999 to join a radical Islamic group. His best friend at Cranford Community College was Asif Hanif, who in 2003 blew himself up in a Tel Aviv nightclub. Officials in Islamabad said that Siddiqui is a close aide of al-Qaeda’s operational commander, Abu Faraj al-Libbi, who was arrested this year and handed over to the US.

This complicated network points to al-Qaeda’s high command having a hand in picking members of the cell who carried out the attacks on three Tube trains and a bus. It also raised questions over why Western intelligence agencies failed to detect this network.

Officials in Pakistan have discovered that Tanweer also contacted members of two outlawed local groups, including Osama Nazir, a leader of Jaish-e-Mohammed, who was arrested last year over an attack on a Christian church in which two Americans died. Their meeting came when Tanweer told his parents that he had gone to see friends and relatives in his father’s home town, Faisalabad.

Jaish is known to operate a network in Britain and one of its earlier recruits was the former LSE student, Ahmed Omar Sheikh, who masterminded the kidnap and murder of the US journalist, Daniel Pearl.

The Pakistani officials said that they passed a warning to Britain about the British-born mastermind who left the country on the eve of the attack. They believe that the unnamed Briton is the same militant who attended a terror summit in March 2004, where the London attack was planned.

Once the Underground was targeted, the recruiting network set out to find its bombers. Police believe that so much explosive was left in the terrorists’ bomb factory in Leeds that there could have been a fifth suicide recruit who lost his nerve at the last minute.

The 10kg of explosive that was found was from the same batch and the same weight that the four bombers had in their rucksacks. One source close to the investigation said: “We don’t believe this cell were just trying to show us they can make as much of this explosive as they want. Other items found in the house also point to somebody else being involved who we can’t trace.”

Detectives are looking for missing friends of the four in the Leeds area. At least two men have not been seen since the eve of the bombing.

The source said: “It could be if there was another bomber he feels ashamed and has gone to ground, or he knows we would want to question him as part of this conspiracy. There are others we need to find such as who recruited these men, who paid for the explosive materials and built the devices, and who gave the orders in the first place.”

Dr el-Nashar, 33, the biochemist who had allegedly rented his flat in Leeds to the fourth bomber, where the leftover explosives were found, denied any links with the London attacks or with al-Qaeda. He insisted that he did not pass on his skills as a chemical engineer to the bombmaker. Dr el-Nashar left Leeds a week before the suicide bombings to spend the summer with his parents, saying that he would be back in September. His family said that he was arrested at their home in a poor suburb.

He had left Leeds on another occasion recently, telling friends that he was visiting Ireland to be interviewed for a university post. On his return, he said that he had been beaten to the position by a highly able Chinese man. University College, Dublin, said that it had no recollection of him. Neither Trinity College nor Dublin City University could confirm or deny whether he had applied.

Dr el-Nashar completed his doctorate at Leeds University in February on the use of enzymes in biotechnology. The Home Office extended his visa so that he could look for post-doctoral work in Britain.

Dr el-Nashar’s landlord said that he had asked him if he could borrow the flat for a friend from London who needed accommodation. Two of the suicide bombers are reported to have had links to the flat but there is no suggestion that Dr el-Nashar knew of any wrongdoing. Neighbours and colleagues described Dr el-Nashar as an exceedingly polite and talented young man.

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