Physically, it is easy to be a terrorist. Killing unarmed people is never frightfully difficult. It is impossible physically to stop terrorism. I commented years ago that the theatre of security at airports just created a new target; the people densely packed queueing for security at airports. It will always be simple to kill individuals, and if you wish to kill a lot of people at once, there are just so many places where people are crowded together. Planes, trains, buses and coaches, metros, ferries and the associated boarding places of all of those. Cinemas, theatres, supermarkets, concerts, bars, pubs, restaurants, cafes, shopping malls, public squares. Lectures, meetings, ceilidhs, churches, mosques, schools, workplaces, tourist attractions. Football matches, firework displays, the boat race, racecourses, carnivals, festivals, beaches, fun fairs, amusement arcades. Commemorations, demonstrations, marches. Cabarets, swimming pools, museums, canteens.

It is impossible physically to prevent all determined terrorist attacks without imposing a level of security which would fundamentally change the very experience of being a human being and the very foundations of human society. The uselessness of it was demonstrated fatuously by Tony Blair sending tanks to Heathrow airport.

But if we cannot physically defend against determined terrorists, what can we do?

Well, the most important thing is, don’t panic. Given how easy it is to kill people physically, the important thing is how extremely difficult it is to do it mentally. In fact terrorism is vanishingly rare. It is so rare there has only been one person killed by terrorists in the mainland United Kingdom in the last decade.

An event like that in Brussels today horrifies and terrifies. But remember, that the same number of people murdered today are killed in Belgium less than every three weeks in traffic accidents, and have been killed at that rate or greater in traffic accidents for over four decades. Over 700 people a year die in traffic accidents in Belgium; twenty times more than have just been killed by terrorists. Of course, the terrorist incident is a big single death toll and more stark because it is a deliberate act of evil. But if you’ve just been mown down by a car, that also is not pretty and you are just as dead.

So panic must be avoided. There is no sense in which the tiny threat of terrorism is a genuine threat to western civilisation – unless we grossly overreact. Old fashioned intelligence work is the best way to counter active intelligence cells. This would be much more effective if it were targeted. The pool of intelligence is far too contaminated with tens of millions of intercepts of harmless people from mass surveillance, and all kinds of dross intelligence fed to us from torture chambers around the world.

Western policy in the Middle East in the last decade has been a grotesque failure by any possible measure. If western states simply stopped inflicting violence and death abroad themselves, it would do much to end the cycle. People are less likely to turn terrorist if they feel they have a worthwhile role in society and something more to live for. It is a truism that alienation of young Muslim men from the societies they live in has motivated several terrorists. That same alienation affects young non-Muslims too, as a generation faces crippling debt, unfulfilling, unprotected and low paid work and an unconsidered life in a society skewed to support the extravagant lifestyles of a tiny minority of the ultra-wealthy. I fear that if society continues the way we are going, political violence of a nihilistic nature will become a more common reaction.

Any response that tries simply to increase physical security and surveillance will entirely miss the point.