A chilling video allegedly showing one of the London suicide bombers and backed up by a top Al Qaeda figure on Thursday threatened more attacks unless Britain pulled its troops out of Iraq and Afghanistan.
The video, showing suicide bomber Shehzad Tanweer, included a statement by Ayman al-Zawahiri, Al Qaeda's second-in-command.
It was first broadcast by the Arabic-language broadcaster Al Jazeera, and extracts were shown on the BBC.
"What you have witnessed now is only the beginning," Tanweer is heard saying.
The attacks would continue until "you pull your forces out of Afghanistan and Iraq," he added, justifying attacks on civilians in Britain because "they voted for the government."
The official spokesman for Prime Minister Tony Blair said the government had no reaction to the video.
"I think we want the attention to focus on the quiet reflection of the nation as a whole and I don't think anything should be allowed to get in the way of that," he said.
The video is seen by security experts as a "last testament" from Tanweer, 22, who was from Leeds, in northern Britain.
The threats added to a feeling of anxiety and unease among Londoners as they prepared to join the whole nation in a minute's silence to mark the anniversary Friday.
"There can be no doubt that the release of the video at this time can only cause maximum hurt and distress to the families and friends of those who died on 7/7 and the hundreds of people who were injured in the terrorist attacks," said Andy Hayman, the assistant commissioner of Scotland Yard.
Altogether, 52 passengers died and more than 700 were injured in the attacks by four suicide bombers on Underground (Tube) trains and a bus in London on July 7, 2005.