During an interview conducted by the BBC with Andrew Parker, head of MI5, it was revealed that the UK is threatened by

more terrorist activity coming at us, more quickly,

while the terrorist threat was at the same time “hard to detect.” The UK has suffered five terror attacks this year alone, which Parker said “deeply affected” MI5 staff. Nevertheless, the tempo of counter-terrorism operations was the highest he had seen in 34-years with MI5, with live operations tracking 3.000 individuals involved in extremist activities in some way. According to the BBC:

Twenty attacks had been foiled in the last four years, including seven in the last seven months, he said – all related to what he called Islamist extremism.

In some cases where terrorists were successful in their attacks, the perpetrator was well known to MI5. Khuram Butt, for example, the perpetrator of the London Bridge attack, had been under investigation by the security services. When asked about the point of surveillance when even someone who had, in the words of the BBC:

made ‘no secret of his affiliations with jidhadist extremism’ [yet] had then been allowed to go on to launch a deadly attack,

Parker answered that the risk from each individual was assessed on a “daily and weekly basis“, but always based on “fragments of information“. That, nevertheless, the likelihood of an attack being carried out by someone “we know or have known” was large –

otherwise it would mean they had been looking ‘in completely the wrong place.

While Parker stressed his agency was trying to learn as much as possible from recent incidents, the growing scale of the threat makes stopping all plots impossible.

We have to be careful that we do not find ourselves held to some kind of perfect standard of 100%, because that is not achievable. (…) Attacks can sometimes accelerate from inception through planning to action in just a handful of days. This pace, together with the way extremists can exploit safe spaces online, can make threats harder to detect and give us a smaller window to intervene.

Renewing a call for more co-operation from technology companies, Parker said technology was “not the enemy.” He did add, however, that companies had a responsibility to deal with the side effects and ‘dark edges’ created by the products they produced. He mentioned, in particular, the online purchasing of goods – such as chemicals – as well as the presence of extremist content on social media and encrypted communications.

Parker also said that more than 800 individuals had left the UK for Syria and Iraq. Some had then returned, often many years ago, and subjected to risk assessment. Recently, fewer than might be expected have returned: those still in Syria and Iraq may now not attempt to come back because they know they might be arrested. Parker revealed that at least 130 had been killed in the conflicts. He also stressed that international co-operation remained vital, also revealing there was a joint operational centre for counter-terrorism. Based in the Netherlands, security officers from a range of countries worked together and shared data, which had led to 12 arrests in Europe.

In terms of state threats, Mr Parker said the range of clandestine activity conducted by foreign states – including Russia – went from aggressive cyber-attack, through to traditional espionage and the risk of assassination of individuals. However, he said the UK had strong defences against such activity.