The scale of Islamist extremism is a problem for MI5

In her statement to the House of Commons, Theresa May said that the man responsible for yesterday’s attack was British-born and had previously been investigated by MI5 ‘in relation to concerns about violent extremism’. However, May stressed that, ‘The case is historic—he was not part of the current intelligence picture.’ 

Now, the fact that the attacker was known to the security services will lead to questions about why a closer watch wasn’t being kept on him. But there is, frankly, a volume problem here. The number of radicalised individuals is now so large — there are several thousand Islamist extremists being monitored by MI5 — that the security services have to be selective about who they keep the closest tabs on.

The weapons used by yesterday’s attacker, a 4×4 and two kitchen knifes, are easily available. It is hard to think of a reason why a member of the public would have reported someone purchasing—or in the case of the car, renting—these items.

We now wait to see whether there was other information that should have prompted concern, social media accounts and the like.