Earlier this year, Boris Johnson failed to mention Islamist extremism during his speech at the Munich Security Conference – perhaps the best-known event on the international anti-terror circuit.

We write what follows amidst claims that the man arrested on suspicion of murdering David Amess had been on the Prevent programme.  But it applies regardless of whether or not this allegation is true, or indeed of the facts of this particular case.

The Prime Minister’s omission was an extraordinary one, as we noted at the time, because Islamist terror is one of the main security challenges we face, and was identified as such in the Government’s recent Integrated Review of security policy.

The strategy also cited neo-nazi, Irish republican and eco-terrorism, but the experience of the last 20 years suggests that Islamist extremism is the most prolific of these in Britain, at least in terms of attacks launched rather than planned.

We make only one point about it today: beware of claims of “lone wolf attacks”. In the main recent Islamist-related cases – the murder of Lee Rigby, the Manchester arena bombings, the London Bridge assaults and others – the culprits were networked.

And even those with no physical proximity to fellow extremists can find online substitutes. This fact will feed into MPs’ suspicion, often sharpened by personal experience, of social media.

It will have an impact on attitudes in the Commons to the Online Harms Bill – in which legislators must balance the protection of the vulnerable against freedom of speech. Getting it right won’t be easy.

Expect to hear more calls for regulation of social media and the internet in tomorrow’s Commons statement in the wake of David Amess’ violent death.

Recognition that Islamist terror “hasn’t gone away, you know” – as Gerry Adams once said of the IRA – is likely to be voiced less prominently from the backbenches.

There is a fashion for denouncing China (which is justified), and a continuing focus on Russia (ditto).  And there’s reason to beware of neo-nazi violence.

After all, Thomas Mair, Jo Cox’s murderer, offered no psychiatric defence at his trial.  And “carefully arranged in a bookcase topped with a golden eagle emblazoned with a swastika, [was] the library of a self-taught neo-Nazi”.

But whatever happened in Southend, Islamist ideology and violence is still with us. Experience suggests that it seldom comes from the hands of “lone wolves”.