How can we gauge the terrorist threat against us? Not easily is the short answer, much as we would like to be reassured that the problem will go away, or even simply know quite how afraid we should be.
One possibility would be statistics. In a report released last week detailing broad trends from 2016 and looking ahead, Europol,the European Union's law enforcement agency, gave a numerical breakdown of fatalities, arrests as well as failed and successful plots.
The report is compiled from data supplied by six concerned nation's security services and is therefore reliable.
Europol point out that violent Islamic extremists in Europe are getting younger, and include more women than previously.
Both trends have been evident to researchers for some time, though the youth of involved in terrorism and related activities is sometimes exaggerated.
Though there are examples of extremist activists who are teens and even pre-teens, the average age remains somewhere around 26, only slightly lower than it was a decade ago. Recent attackers in London, Manchester and Paris have included a 22 year old and a 52 year old. Women are involved in more attacks, especially by Islamic State, but still make up a fraction of the total.
Arrests for violent extremism have risen, but the number of overall “failed, foiled or completed attacks” is down, from 211 in 2015 to 142 in 2016. What is most striking perhaps is that both years saw the UK at the top of the table for total number of plots by country. Particularly given the high number of casualties in France – more than 230 over two years - what could this mean?
One conclusion is that the British secret services are very good, and have successfully thwarted a very significant number of attacks.
This is in part true – MI5 and particularly British police forces are recognised as world leaders in counter-terrorism.
Something clearly went badly wrong this year however with three attacks in two months. At the strategic level, the changing nature of the threat appears to have caught the UK services off-guard. At a more tactical level, intelligence sharing with overseas partners appears to have broken down in at least two cases, allowing attackers to complete planning which would probably otherwise have been stopped.
A second conclusion is more worrying. It is that the level of the threat from terrorism – predominantly jihadi in nature, though there is rising rightwing activity too – has been high in the UK for many years and that a degree of complacency may have crept in to policymaker's calculations and the broader public perception.
While the media spilled much ink in examination of the flaws in the French model of assimilation following the terrible attacks in France in 2015 and 2016, for example, there was less focus than perhaps there should have been on growing extremism, violent or otherwise, in the UK.
The high numbers of young Frenchmen, and some Frenchwomen, heading to Syria to join the Islamic State were indeed impressive, but, as the most recent Europol report indicates, it is the “stay at home” jihadis who are the problem now.
And the UK apparently has plenty.Can we project future trends? Perhaps, by looking at the past.
Ten years ago Europe suffered another surge of Islamist-inspired violence. As today, this started on Europe's frontiers – in Turkey, Tunisia and Morocco – before moving across the continent – to Spain and Holland first - and then eventually to the UK in 2005.
This proved the high point of the violent tide, which then steadily ebbed over the following years. This decline was due to security services learning fast, governments making better decisions, the fading of the US-led “War on Terror” with its attendant excesses, and the revulsion inspired in local Muslim communities by violence committed in their name.
Everywhere, whether in the Middle East, South Asia or Europe, surveys showed that the experience of Sunni Salafi jihadi violence on local streets led to massive loss of support for al-Qaeda. Osama bin Laden eventually recognised this, mulling a rebranding of his group shortly before he was killed in 2011.
It is possible we are seeing the peak of this tide of violence too, and that it will ebb too in the same way. Any optimism has to be tempered however. The threat declined, certainly, but remained at a level which was significantly higher than it had been before, say, 2001 and the 9/11 attacks. The same is likely to be true if this current terrorist surge loses its power.
Each wave of violence leaves its bloody debris of radicalisation and polarisation on the shore,and so the next wave surges even higher.
