By Dominic Casciani
Home affairs, BBC News
British al-Qaeda plotter Dhiren Barot - someone with extraordinarily detailed plans to kill - was jailed for life this week.
Eliza Manningham-Buller: Frank assessment
The plots were as ambitious as they were shocking.
But in the wake of that terrorism conviction, and a highly-nuanced speech from the head of MI5, it's worth noting that the feeling of shock does not just affect the majority in society.
Right at the heart of this storm are fearful Muslim communities in which individuals are trying to comprehend the threat.
And so while MI5, the police and others press ahead with counter-terrorism work, the real battle is how to undermine the ideology used by extremists to tempt youngsters to their cause.
Dame Eliza Manningham-Buller's speech warned of the scale of this task - 30 suspected plots, 1,600 individuals.
"More and more people are moving from passive sympathy towards active terrorism through being radicalised or indoctrinated by friends, families, in organised training events here and overseas, by images on television, through chat rooms and websites on the internet.
"My service needs to understand the motivations behind terrorism to succeed in countering it, as far as that is possible. Al-Qaeda has developed an ideology which claims that Islam is under attack, and needs to be defended."
The MI5 chief's analysis indicates the huge problems that the government, security services, Muslim communities and wider society face in getting a grip on the mechanisms of radicalisation.
Crucially, there are grave concerns in some parts of government and among communities themselves that there is neither a consensus nor a clear strategy in how to reach out to those within networks or to stop others signing up.
The most pessimistic analysis is that the security services don't really know what they are looking for - while the communities themselves are too divided to know how to spot it when it's happening.
British Muslim communities and organisations are essentially split over radicalisation.
There is a small minority of extremists - some are genuine security threats, others may be little more than temporary fellow-travellers. The security services fear the balance may be tipping towards the former.
Then there are many, particularly among the older mosque leadership, who are in denial.
Even after the compelling video "wills" of Shehzad Tanweer and Mohammed Siddique Khan, two of the four London suicide bombers, it is not hard to find people in positions of community authority who deny that terrorists are targeting young people in their midst.
Finally, there are the growing number of British-born, middle class Muslims who are actively trying to reclaim the debate on their faith, amid fears for a lost and confused generation.
Al-Faisal: Key radical preachers jailed - but damage already done?
Many of this group fear Britain may be acting 15 years too late. Self-appointed preachers such as Abu Hamza and Abdullah al-Faisal, both in jail, may have already done their work.
Amid all this is a majority of ordinary Muslim folk sick of what is going on, confused about how to react politically and yearning for a more banal life.
Amid these internal tensions, policy-makers and the security services are also trying to influence debate and reduce the threat of extremism but it is proving extremely difficult.
Many young Muslim leaders believe that the extremist threat is a generational challenge which requires a step-change in engaging with the young - and that the state - and the older leadership in their own communities - have failed to get a meaningful grip.
While that may be a gloomy assessment, it does at the very least suggest that these leaders and the likes of MI5 are talking similar language, mapping out the same challenge.
In her speech, Dame Manningham-Buller made it clear that none of these problems can be tackled by MI5 alone.
Many Muslim leaders feel under pressure to deliver - but they're not sure what government wants - or whether they themselves can deliver anything at all
"Others have to address the causes, counter the radicalisation, assist in the rehabilitation of those affected, and work to protect our way of life," she said.
Community leaders are indeed grasping for solutions. Barely a week goes by without yet another round of Whitehall meetings. Some deradicalisation projects are being piloted.
But there is also frustration with government. Many Muslim leaders feel under pressure to deliver - but they're not sure what government wants - or whether they themselves can deliver anything at all.
There is simmering anger that the 64 recommendations in the Muslim-led Preventing Extremism Taskforce, set up after the London bombings, have got bogged down in the government machine. Only one of the proposals, a roadshow of scholars, has had any impact to date.
Ministers reject this charge, saying that many of the recommendations are being acted upon. Communities secretary Ruth Kelly has also launched the Commission on Integration and Cohesion.
That commission will not report until next year. For many at the sharp end of trying to challenge Islamist radicalism, time feels like it is slipping by.