In this new phase of "franchise terrorism", al-Qaeda has been described as an idea rather than an organisation - "a global movement infected by al-Qaeda's radical agenda", as Mr Tenet put it. Even if its structure has been disrupted by military action, arrests and increased security, it still acts as an inspiration to groups, from Chechnya to the Palestinian territories, that have minimal contact with the network.

They may also hire outside help — a trend branded as "franchise terrorism", which was used in the Casablanca and Riyadh bombings earlier this year. Kevin Rosser, one of the report's authors, says that, "like stepping on an anthill", the fall of Afghanistan has caused al-Qa'ida agents to flee, creating a militant diaspora.

Osama bin Laden is either dead or on the run, but the thousands of terrorists who trained in his camps remain a continuing threat. Their "sleeper" cells have blended into community life in countries around the world, including the United States, awaiting only directives and financing to strike again.