Intelligence agencies have had some success in tracking suspected al-Qaeda operatives. But the organisation is changing to continue its fight against the West.
By Peter Taylor
Reporter, Third World War: al-Qaeda
The West has never encountered an enemy like al-Qaeda before.
The fear is that an attack will come in the UK
The problem for the world's intelligence agencies is that it is not a unified organisation with an identifiable structure, like the IRA, but an amalgam of groups around the world whose members embrace Osama bin Laden's ideology of global jihad, or holy war.
These Jihadi warriors share the belief that they have an obligation to fight the oppressors of their Muslim brothers, from Palestinians in the Middle East to Muslims in Chechnya. And to all Jihadis, the chief oppressor is the United States, a nation they regard as the "Great Satan".
A detailed examination of the Algerian terror network in Europe illustrates the enormity of the intelligence task.
The initial breakthrough came over Christmas 2000 when the German equivalent of the SAS burst in on a flat in Frankfurt. They arrested four men and uncovered an arsenal with bomb-making chemicals, weapons, cloned credit cards and false documents.
The men were all finally convicted of plotting to bomb Strasbourg. What was believed to be a reconnaissance video was found in the flat, its most prominent feature a lingering sequence on that city's famous Christmas market. That, investigators believed, was the intended target. If the bomb had gone off, there would have been carnage.
Jihad warrior in the UK
The four prisoners were Algerians whom German investigators refer to as unaligned mujahideen, rather than al-Qaeda members. Nevertheless, according to David Veness, the head of Scotland Yard's counter-terrorism unit, this Algerian network has been "a key dimension of the al-Qaeda agenda within western Europe".
When I interviewed the Frankfurt cell's alleged ringleader, Salim Boukari, in a German top security prison, he said he did not want to talk about the 11 September attacks or Osama bin Laden.
Salim Boukari with Peter Taylor
He said he was a Mujad - a holy warrior. Boukari had been living in England on and off for almost 10 years and another of the plotters, Lamine Maroni, had been living in Sheffield as an asylum seeker. MI5 and Special Branch appeared to know next to nothing about them and both had got under the wire.
Working closely together, Europe's intelligence agencies began to piece the complex network together.
The French had bitter experience of Algerian Islamic extremists, and had fought them for many years after their offshoots had carried out a series of bombings in Paris and Lille in the mid-90s.
There were several attacks in France in the 1980s and 1990s
The intelligence built up over this period by the French proved invaluable. The role of the UK's MI5 and Special Branch was also crucial since many Algerian extremists had sought refuge in London after the crackdown in France. The centre of the network was believed to be in London.
Investigators were even more alarmed when they discovered that its tentacles crossed the Atlantic to Canada and the US, where cells had been planning to blow up Los Angeles International Airport on Millennium Eve, 1999. The would-be bomber, another Algerian, Ahmed Ressam, who trained in Afghanistan, was arrested and the plot was foiled just in time.
But was the hand of al-Qaeda behind the network?
What appeared to be conclusive proof came from Italian intelligence agents who intercepted a phone call from Milan to Afghanistan. It was made by a suspected Egyptian terrorist, Es Sayed, who had fled to Italy.
He's believed to have been calling Abu Zubaydah, one of al-Qaeda's senior military commanders and the holder of the keys to the Afghan training camps. Italian intelligence concludes that Es Sayed had been sent to Europe by al-Qaeda to radicalise and recruit young Muslims for Osama bin Laden's holy war. Es Sayed is subsequently thought to have been killed fighting for the Taleban.
The problem for the intelligence agencies is that they're now dealing with an enemy that has restructured in response to the setback it has suffered.
It now operates in autonomous cells that can change shape and tactics at will. Finding and neutralising them before they can strike is even more difficult. And the greatest fear is that a suicide bomber, a lone wolf, will emerge.
As David Veness chillingly warns, an attack on the UK is not a matter of if but when. I asked him how long the war would last. "Years," he said.
Third World War: al-Qaeda is broadcast in the UK on BBC Two on Tuesdays 10, 17 and 24 February at 2100 GMT.