The Iraqi-based group, which is also holding three other Christian hostages, said that American and Iraqi authorities had a “last chance” to save the captives by releasing all Iraqi prisoners.

The new video, said to have been recorded on January 21 and broadcast yesterday on the Al-Jazeera television station, surprised British authorities who feared Kember had been killed before Christmas.

The Foreign Office said yesterday it was “studying” the new video, which shows Kember dishevelled and grim-faced but otherwise in apparently reasonable health. It is the first news of the hostage since December 10 when the kidnappers’ previous deadline expired.

One of Kember’s friends, Sue Claydon, said yesterday it was “wonderful” to see evidence that he was still alive. “When the abduction took place, a number of people asked how we thought Norman would cope,” she said. “At the time I said I felt he was a rational, sensible man, and also a man of great faith, as is true of the other three men.”

Kember, a grandfather from Pinner in northwest London, travelled to Iraq in November with Christian Peacemaker Teams, a Canadian-based organisation, to promote peace. However, the former medical physicist was captured in Baghdad along with two Canadians and an American on November 26, just four days after his arrival.

He was paraded by the previously unknown Swords of Righteousness Brigade which is thought to be linked to Abu Masab al-Zarqawi, the head of Al-Qaeda in Iraq.

The group demanded the release of all Iraqi prisoners and the removal of coalition troops from Iraq.

The initial two-week deadline was extended by 48 hours amid international outrage over the capture of peace campaigners but nothing more was heard. Kember’s plight won sympathy even from terror suspects, who appeared on television to condemn the kidnapping.

Abu Qatada, who has been described as Al-Qaeda’s ambassador in Europe, issued a statement in Arabic from his cell in Full Sutton prison near York, which said: “I, your brother Abu Qatada . . . beseech my brothers in the Swords of Righteousness in Iraq, who are imprisoning the four Christian peace activists, to release them in accordance with the fundamental principle of mercy of our faith.”

Earlier this month, Kember’s wife Pat made a renewed televised plea to his captors via Al-Jazeera. “He is a very good, caring man, always helping others,” she said. “He has been a pacifist all of his adult life . . . He and his three friends are totally against the war. They went to Iraq on a peace mission to listen to and, if possible, to help Iraqi people.”

A vigil for the four captives was held in Trafalgar Square on Thursday evening to mark two months since they were taken hostage but hope had all but evaporated.

More than 250 hostages have been taken since 2003 and at least 39 have been killed.

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