Pakistani intelligence officials told AP and Reuters that Taifi, the detained Saudi, played a role in the 2005 attacks in London, when four British Islamists carried out suicide bombings that killed 52 people. Some of the bombers had visited Pakistan and trained with militants there.
British and American intelligence officials say they have accounted for most of the senior Al Qaeda operatives allegedly involved in planning the July 7 attacks from Pakistan.
Abdul Hadi al-Iraqi, the man said to have planned the attacks, was captured in Turkey in 2006 as he was travelling to Iraq in a bid to improve relations with terrorists there.
His associate, Abu Munthir, who acted as a contact between terrorist groups and Al Qaeda's senior command, was detained in Pakistan in 2004.
The bomb-maker is said to be a man called abu Ubaida al-Masri who is thought to have died from hepatitis C last year.