Experts now believe that the Madrid bombing of 2004 was a blueprint for the London attacks. For the first time, many key figures hunting the Madrid bombers agreed to talk, including the Spanish investigator leading the hunt for the rest of the Madrid cell. Award-winning journalist Peter Taylor was also given access to crucial intelligence reports and had private briefings with Britain’s own security services.

A crucial finding is that al Qaeda hasn’t gone away - it’s just shut down its head office. Local branches have opened up in its place and act autonomously, which means they’re much more difficult to identify, infiltrate and catch. Some of the men involved in the Madrid blasts acted more like playboys than jihadis.  But that’s what made them so dangerous. They looked ordinary. They were part of the new al Qaeda that succeeded the Afghanistan generation. 

This investigation also reveals how the internet rescued the international terror network from oblivion. It’s an underground broadcasting network for gruesome propaganda videos, a secret and safe means of communication and a bottomless online library of training manuals and terror know-how. Combined, these elements make the net the most significant weapon in the movement’s new fractured and decentralised state.

The current state of al Qaeda and the health of al Qaeda is largely due to its ability to manipulate the internet – Mike Sheuer, former head CIA Bin Laden Unit.

This expose makes for fascinating viewing. The BBC has beaten off stiff competition from rival broadcasters to secure unique and unprecedented access to all the agencies at the centre of hunt for al Qaeda.