Writing about terrorism is to enter into a field of more uncertainty than in most journalistic work. The basic uncertainty in the present context is over the intent and capacity of the main terrorist networks. We know that the Islamic State (ISIS) is brutal, since they take pride in demonstrating brutality. But we don’t know how far they will go.

Writing about contemporary terrorism truthfully requires taking up a position on that. That position is not in itself the truth: but it is a declaration of the assumptions the writer makes when commenting, or reporting. It is what the writer believes to be the underlying truth of the threat faced (he may, of course, be wrong. In this case, I hope I am).

In interviews with secret service people, mostly retired, for a forthcoming book (Journalism in an Age of Terror: I B Tauris), I often heard that senior British officers had thought the phrase “War on Terror” to be a stupid one, and that they never used it. It was not a war, they believed: the struggle was not – the word was used quite often – an “existential” struggle. It was a serious challenge from serious terrorists: hard, vicious - but finite.