By Gordon Corera
BBC security correspondent
The latest video from the al-Qaeda leadership is being studied closely in Washington and London for clues about the organisation's strategy and possible whereabouts.
Al-Qaeda leaders may be trying to claim credit to boost their position
It is not, however, being seen as conclusive proof that Osama Bin Laden or his deputy were directly involved in either planning or executing the London attacks.
The 7 July bombings were said by police to bear the "hallmarks" of al-Qaeda but that could still mean the bombers were inspired and influenced, rather than directed, by it.
The Ayman al-Zawahri video does not include a direct claim of responsibility for London - although al-Qaeda videos rarely, if ever, contain such statements.
British intelligence agencies and police investigators have been trying to follow the trail of the 7 July bombers to see if it leads to the al-Qaeda leadership, but they say so far no conclusive evidence has been found.
It could still be found at some point but any links unearthed are more likely to be indirect.
The video message is being interpreted more as an opportunistic attempt by al-Qaeda to exploit the London attacks as a vehicle for pushing its own agenda.
Some analysts even believe al-Qaeda's leadership could be trying to claim credit for something others have carried out, because it's important for it to show itself as still the leader of the jihadist movement.
Despite being heavily damaged since 2001, al-Qaeda needs to show it is still around and active in order to maintain its reputation and draw in new recruits.
Claiming ideological and spiritual sovereignty over the attacks is therefore important for it in order to maintain its self-image as the leading, guiding force of jihadist opposition to the West.
After tying the London attacks to Tony Blair's foreign policy and warning of further harm, the statement moves into far more traditional rhetoric that has been seen in previous messages, with the demand to leave Muslim lands and the focus on Iraq.
The message does show an acute understanding of the nature of the information war and the news agenda.
While earlier messages were directed largely at the Muslim world, more recently they have also targeted western public opinion in an effort to divide it from its political leadership.
In this case they bring up the issues of British involvement in Iraq and US casualties, knowing full well that these are difficult questions for Tony Blair and George Bush.
US and British officials are increasingly focused on fighting the ideological battle against al-Qaeda as well as the military conflict, focusing on the need to counter its propaganda.
Were the 7 July bombers working with, or influenced by, al-Qaeda?
In many ways the battleground here is Muslim youth in the West and the fear that, unless properly countered, statements like that of Zawahri will contribute to radicalisation and recruitment, sustaining the long-term threat.
Al-Zawahri's last message came in June and was focused on Egypt. A month later suicide bombers struck hotels at the Sharm al-Sheikh resort.
No one is sure whether these messages act as triggers for other groups to attack but that possibility may cause some concern for British officials.
Even if there is no third group ready to attack, the concern will be that other groups may take their cue from the message and try to put some kind of operation together.
"When Zawahri goes public and says 'conduct more attacks in London' there will be people that will attempt to do it," argues former CIA officer Robert Baer.
Every day the Joint Terrorism Analysis Centre - housed inside MI5 - assesses the intelligence over the threat.
The message will be factored into the assessment but is thought unlikely to make any significant difference to its overall view.
However that will not prevent the message being taken seriously as another salvo in the ongoing campaign.