A video in which one of the London suicide bombers warns of further attacks was broadcast on al-Jazeera television yesterday.
The footage of Shehzad Tanweer threatens to overshadow today's programme of official events marking the first anniversary of the July 7 terrorist attack.
A Whitehall official said: "The terrorists have put this out to gain maximum publicity for themselves and maximum pain for the survivors and the bereaved."
In the video, the Yorkshire-born British Muslim warns that the London bombings would be followed by a "string of attacks that will continue and become stronger" until British troops withdraw from Iraq and Afghanistan.
Its linkage of the bombings to British foreign policy appears to be a calculated challenge to the government of Tony Blair, who earlier this week urged British Muslims not to excuse extremism by blaming British military operations abroad.
Tanweer, 22, from Beeston in Leeds, killed himself and seven innocent people, injuring many others, when he detonated a rucksack bomb on an Underground train near Aldgate station.
Today's programme of events marking one year on from the bombings on the capital's public transport system, which killed 52 innocent people, includes a nationwide two-minute silence at midday and an open-air service in Regent's Park in the afternoon.
Only three days ago, one of the most senior anti-terrorist officers admitted that police had still not been able to establish who first radicalised the four bombers.
Although an official report into the attacks contends that the bombers acted alone, Peter Clarke, head of the Metropolitan police's anti-terrorist branch, said police were still looking for evidence that might support suspicions of a more complex terrorist operation.
While Tanweer's statement was recorded more than a year ago, the tape in which he features was aired publicly for the first time yesterday on the Qatar-based Arab television network after being announced on an Islamic website.
The timing of the video was not predicted by Whitehall or the police, although officials claimedits existence and its tone came as little surprise. The release of an earlier video last September of Mohammad Sidique Khan, the suspected ringleader of the London attacks, led security and intelligence officials to assume that there would be a second video broadcast eventually.
Tanweer had come from a similar background to Khan, and was thought to have been acting as his main support in planning the attacks.
Investigators have been working on the likelihood that the two videos were edited and added to following the London bombings, lending weight to the theory that while carried out by "home grown" British Muslims, the planning of the attacks involved a wider conspiracy linked to the loose international network of Islamic terrorists.
