The additional footage is believed to include the gang’s leader, Mohammad Siddique Khan, directly confessing to the attacks on London which killed 56 people. Another of the cell, Shehzad Tanweer is also said to appear, according to a source involved in obtaining the film for the Arab satellite channel, Al-Jazeera.

Police and intelligence experts who were yesterday studying the material, have asked the TV station for all the footage they have on Khan and from al-Qaeda’s second in command, Ayman al-Zawahiri.

In his video, Osama bin Laden’s deputy describes the July 7 suicide attacks as “the blessed London raid”.

He also accuses Muslim leaders in Britain of taking orders from the Queen, calling them “scholars of beggary” who work “to appease Elizabeth, the head of the Church of England, imitate her and issue fatwas in accordance with her religion”.

The concern is that whichever radical group is in possession of the British bombers’ film intends to maximise the propaganda value by releasing more of it over the coming weeks.

Ayman Gaballah, the deputy chief news editor at Al-Jazeera, denied claims they have footage by any of the other three London bombers.

Scotland Yard knew about the existence of Khan’s video testament before it was publicly known that al-Jazeera had been sent the tape by unidentified militants. Counter-terrorist detectives and intelligence agents are trying to determine where and when it was made.

They are also working abroad to uncover whether it was smuggled out of the UK by another member of the cell or electronically transmitted to radical sympathisers who produced the edited version.

Sir Ian Blair, the Metropolitan Police Commissioner and Jack Straw, the Foreign Secretary, have said they believe the attack bears the hallmarks of al-Qaeda but the Khan tape is still not seen as conclusive proof that it was directly ordered by the network’s high command.

Detectives believe that the July 7 bombers did have outside help, including from known militants in Pakistan whom Khan and Tanweer met during their three-month visit to the country this year.

Forensic experts are “pulling apart” the tape to analyse any background clues but they realise that part of the training for would be suicide bombers is how to disguise where the film was made.

Police are also searching for the last testaments of the other two bombers, Hasib Hussain and Jermain Lindsay.

Yesterday the video brought condemnation from MPs of all sides, Muslim community leaders, survivors and victims’ relatives. The families of the bombers remained in hiding.

Shahid Malik, the Labour MP for Dewsbury, described Khan’s family as “very, very distressed, living in fear”.

Young Muslims in in Leeds and Dewsbury acknowledged the four’s guuilt yesterday; many had previously refused to believe that they carried out the bombings.

Mr Malik joined worshippers at Friday Prayers at the Hardy Street mosque in Beeston where Khan, 30, the ring’s recruiting sergeant, first met Tanweer, 22, and Hussain, 18. “Now they have heard from the horse’s mouth,” Mr Malik said. “Let’s hope people now snap out of their world of delusion.”

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