When it comes to Islamic terrorist plots, Britain faces "a pace [of threat] we have just never experienced before."

Those aren't the words of a politician, but rather the warning of an officer from Britain's domestic spy agency, the Security Service (also known as MI5).

Just before Christmas, Britain's parliamentary Intelligence and Security Committee released its 2016-2017 oversight report on the nation's three main spy services; the domestic-focus Security Service, the foreign-focus Secret Intelligence Service, and the signals intelligence agency, Government Communications Headquarters.

And the report had much to say about the fight to prevent ISIS attacks.

"The scale of the current threat facing the U.K. and its interests from Islamist terror groups is unprecedented." The intelligence committee report continued, "This threat is predominantly driven by the activities of [ISIS] in Syria and Iraq, which seeks to maintain the group’s image and narrative of success in the face of military losses."

But what does the threat look like as we enter 2018?

Well, it's varied between directed, influenced, and inspired operations.

On the directed side, the ISC notes that ISIS retains a "prioritization of so-called external operations." In the vein of the November 2015 Paris attacks, these plots involve ISIS officers in Iraq or Syria deploying attackers with the training and plans to carry out atrocities on British soil. But while the directed-attack threat is higher in continental Europe than in Britain, it is no small issue in the U.K.

Referencing increasing threats from ISIS affiliates in the Egyptian Sinai, the ISC notes an alarming sense of confidence: "Other targets are increasingly being viewed as viable by the group." This bears consideration in light of ISIS' 2015 record in blowing up a Russian airliner over the Sinai Peninsula.

Regardless, as I noted in January 2016, December 2016, and September 2017, Britain's counterterrorism posture reflects a guarded expectation of ISIS-directed attacks on its soil. The recent near-success of Australian and Russian ISIS cells (and perhaps also French and German cells) also evidences why Britain can't let its guard down.

Perhaps reflecting this external direction concern, the report clarifies that MI5 now takes the lead in many international counterterrorism operations where there is a nexus of threat against the U.K. homeland. Foreign operations are traditionally the remit of MI6, but MI5's increasing responsibility in this area reflects its need to counteract complex international plots affecting U.K. territory. The broader takeaway here is that MI6 and MI5 are operating with an increasingly symbiotic relationship.

But that's just one side of the threat picture.

Then, there are those individuals who are either influenced by communications with an ISIS officer or inspired towards attack by ISIS propaganda. For Britain, these are the core ISIS-related threats. An MI5 officer told the ISC that it faces so many threats it must "operate according to what we call a weekly grid, which is a top [redacted number of] investigations week by week that need the most resource [redacted]."

Here, MI5's concluding redaction likely refers to the deployment of 24 hour / 7 days a week human surveillance teams. These teams are deployed to watch every move of those suspects who have been assessed to pose the most imminent threat to the public. However, due to the need to maintain secrecy in surveillance, each team has to be around 20 persons strong. The grid system illustrates the immense challenge MI5 officers face in being forced to stretch resources: If they make the wrong choice, a terrorist attack might occur.

Be under no illusions, the choice is hard. "MI5 also told us," the ISC says, "that it had around 3,000 subjects of Interest on its radar, sitting on top of a larger pool of 20,000 individuals who had previously been subjects of Interest."

That might seem a big challenge in and of itself, but the ISC explains it has been exacerbated by a relatively new development: what an MI5 officer says is a "shift to default encryption and multiplicity of apps that provide secure communications." Those apps take a lot of skill and capability to hack.

Remember all of this the next time someone tells you ISIS has been defeated.