The amateurishness of the attacks is scant consolation

The problem for anyone investigating al-Qaida, whether journalist, intelligence agent, police officer or policymaker, is that most of the time, there is so very little to go on. There is "chatter", there are reported threats, there are videos released, there are small groups of young men who meet to talk and pray, even to imagine aloud terrorist attacks. The threat remains potential or, given the role the internet now plays in interaction between militants, virtual.

Then, suddenly, it becomes very real. There is an event, an actual bombing or a plot that is clearly serious, and it is uncovered and dismantled. There is a sudden media glare and a series of arrests, and then all goes quiet again.

With the massive boost in legal and practical capacities they have received in recent years, the police and security services now say they are confident that in theory they have the powers and capabilities to deal with most threats. The problem is that all the disparate elements that make up their new capacity, ranging from new legal powers and more personnel to increased public awareness, can only be focused on the problem for short periods of time, when Islamic militancy surges from the virtual into the real world.

Those charged with keeping us safe do, however, hold one card that they did not 10 or even five years ago. In the aftermath of 2001, twisted by the paradigms of the cold war or fighting the IRA, analysis of the complex, evolving and dynamic phenomenon that is modern Islamic radicalism was poor. Initially, those who spoke of "al-Qaida the idea, not necessarily the organisation" were dismissed as leftwing cranks. Now, even the head of the US department of homeland security speaks of a tripartite division of al-Qaida into "the hardcore, the associates and the ideology". The question is now which combination of these three elements, these three al-Qaidas, is responsible for the recent attacks.

It seems clear that the events in London and Glasgow were linked. Neither planned strike was particularly professional - bombs in Afghanistan and Iraq are usually far more sophisticated than the devices found in London. Neither detonated as intended, and the mixture of petrol and gas cans, apparently without plastic explosives or ammonium nitrate fertiliser, only tends to work if, as in Afghanistan or Iraq, you have a ready supply of semi-dismantled mortar bombs to chuck in with them.

Driving a car full of inflammable liquids into the front of an airport is equally amateurish. The vehicle was apparently hampered by bollards, a potential problem that an elementary reconnaissance would have picked out. The Glasgow bombers may have acted precipitately out of fear of discovery. This would bolster the theory that the attacks were linked. Strikes in the West End of London and in Scotland would show the supposed reach of the bombers.

We could be dealing with individuals who were newly arrived in the UK - competent but lacking the necessary local knowledge to source what they needed. Or we could be dealing with people who knew Britain well but lacked the competence.

Sadly, such amateurishness is not necessarily a good thing. We know already that the al-Qaida hardcore of Osama bin Laden and the few dozen senior militants around him has been seriously degraded in recent years. Experienced, competent bombmakers are now few and far between. But in their place has arrived a new wave of young men who have been radicalised by al-Qaida's propaganda.

Al-Qaida has traded competence and discipline for resilience and dispersion. Both are effective in their way. Indeed the latter may be the only way to successfully wage war or a guerrilla or terrorist campaign in the 21st century. The obvious parallels with contemporary western military's theories on "fourth generation warfare" (in which one side does not "stand up and fight fair") have actually been underlined by recent radical militant thinkers. This means that although the threat has evolved it remains relatively constant, and relatively severe.

Some of the new adepts are young enough for 9/11 to be almost a childhood memory. Some are prepared to act, sometimes with extreme violence. Nobody needs direction as to what might make a good target any longer, and although skills training is useful, it is not essential. The point can be made without necessarily bringing down a passenger jet. Once again, there is a tendency to look outside Britain for masterminds pulling the strings. Most of the strings are tangled, however. As 7/7 showed us, Bin Laden doesn't need to send anyone to Britain. There are enough people prepared to act who are already here.

Is recent UK foreign policy to blame? Certainly, a serious threat existed before the invasion of Iraq. But it became worse afterwards. And MI5 is braced for more - it is only too aware that, with the US largely inaccessible, Britain has become a next best target.

Jason Barke, the author of Al-Qaeda: the True Story of Radical Islam.