GCHQ intelligence officers Ben and Sunny spoke exclusively to Sky News Defence Correspondent Alistair Bunkall about the threats facing the UK and their efforts to stop them.
AB: What does an analyst do?
Ben: An analyst will do anything that is required to try and find an individual target, as long as they operate within the law.
On a day-to-day basis, that can involve working with partners, that can involve working with our customers in London, that can involve doing the high-end analysis, to actually try and find our targets and do that work.
AB: You talk about partners and customers - it sounds a bit like a supermarket. Who are your partners and who are your customers?
Ben: Partners would be some of our US counterparts. For example the NSA is a partner that we obviously work quite closely with.
Then there's obviously other UK intelligence agencies - MI6 and MI5. Our customers would be anyone in Whitehall really.
AB: Islamic State are well known for their capabilities technologically and their use of the internet in order to propagate their message. As an analyst at GCHQ, what sort of challenge has IS presented you that you hadn't already seen from terrorists like al Qaeda, for example?
Ben: They are a very advanced adversary in that regard, as you allude to. But there are a number of other technological challenges that we as an organisation face.
We always have done - that is the history of GCHQ and our forerunners at Bletchley Park. There's been a huge amount of technological change that we've had to keep abreast of, so yes, Daesh have pushed the bar and raised the bar in terms of some of the technology that they've used and the ways in which they've used it.
But the next adversary will do something else that's different and its keeping pace of that which is always the challenge we face.
AB: Is most of your work looking at individuals who are in the Middle East and North Africa, or are you also looking at individuals in the UK who connect with others in the Middle East?
Ben: My primary role is looking at individuals in the region. There are other people in the organisation who look at others who are potentially coming back to the UK and pose threats to the UK.
AB: Do you run the risk of ever making it personal? Do you follow targets, do you investigate targets, and get to know them, their habits, perhaps even their family lives?
Sunny: That can happen. It really does depend on the targets but also our level of access.
What is it that we are actually following somebody for? What level of detail do we need? We won't try to find out everything about everyone, every single aspect about something, if we've already got what we need. But it can happen. You get to know your targets pretty well.
AB: Given your focus on the Middle East and North Africa, what is your role when a terror attack happens in this country that has connections to that part of the world?
Ben: The first thing is understanding exactly what the situation is - what has happened and what do we know?
So actually getting that ground truth.
Fact-finding is the first thing we will always do. From there, it is understanding exactly how that has happened and where have we potentially missed something in particular, or have we missed something in particular?
Were we expected to know a particular case had happened in a certain way? From there it's very much a case of piecing back that track and trying to put that breadcrumb trail back together to work out exactly what happened and who in the individual countries in question were involved in that.
Does that then give clues about others involved who we could then pick up to potentially stop other things happening at other times?
AB: When you hear of a major terrorist attack, what immediately goes through your mind?
Ben: Obviously there is a huge amount of thought to those involved. That's always the first thing when something happens: 'Okay this is real, there are individuals who are affected by this.'
That re-doubles our efforts to actually keep trying, keep working, let's keep finding these individuals to stop them doing what they're trying to do to harm the UK.
More often than not we are working in Cheltenham, and that's something we're trying to track our targets and understand their motives.
When an attack happens, or a real world event does happen, that really brings it home, that actually this is the importance of this job, this is why we're doing it.
And then when you see the follow on successes of things we have stopped, it brings a huge amount of joy and it really makes working for this organisation worthwhile.
Sunny: I think there's a really well understood purpose. Everybody knows what they're in the office to do. Everyone shares the same common goal.
I think the biggest feeling in the office is one of wanting to go after the targets and find out who's involved. Is there another threat that we need to know about? And are we pursuing somebody that we need to pick up or question? It's basically one of purpose really.
AB: What is your role in the hours and days after an attack? How can you bring value to the role and help keep Britain safe?
Sunny: We're always working really closely with MI5 and MI6. The desks will be taking a really good understanding and a good picture of what's happened and the questions that we need to answer.
We'll jointly agree what questions need to be answered and then we'll have to determine how do we go about actually answering those. What targets do we need to pursue to be able to answer those questions?
And then it's a matter of basically divvying that up, volunteering to say I want to go for that one, and then running the operation from here. Then that close joint working with MI5 and MI6 and always making sure that everything we do is to answer those questions.
AB: Is it exhilarating?
Sunny: It can be. It can be tiring. But, when you have a team of strong analysts and a lot of the people I work with I'm lucky enough to say they're my friends as well.
And when you're working together on a common objective going after targets that everybody knows why we're going after them, it's actually hugely rewarding so even though you're tired your pushing each other.
AB: Although Daesh (Islamic State) has lost large swathes of its territory in recent months, they exist as an organisation still, and an ideology. As an analyst for that part of the world how would you assess the current state of IS and any threat they might still pose to this country?
Ben: I think for me, the key thing to note, is the focus on Daesh. You can eradicate one threat but there will be another threat around the corner.
So for me, as an analyst, it's trying to understand 'OK what has happened and what else is going to come along next that we need to be worried about?' It's only a few years ago our focus was heavily on AQ, we've now moved to Daesh. What is going to be the next threat? What else is going to come along? So we need to be mindful of the wide set of threats that potentially going to harm UK interests.
AB: What is going to be the next threat?
Ben: Good question. We'll see and we'll be there when it comes.