“Thankfully, assassinations are incredibly rare,” she said, partly because of the huge efforts the Security Service puts in the thwart them. “MI5 is interested in state-sponsored, state-backed activity and we look at that in terms of the intelligence we receive.”

Britain expelled dozens of Russian diplomats as a consequence, but Director K said: “Russian state activity – not Russia itself – remains a threat. 

“We would prefer that was not how Russia chose to engage with the world. It is also in Russia’s interests to have positive relations with the world.”

‘I look at where can do our utmost to prevent harm’

Similarly, Director K called out the ransomware attacks that threatened to bring parts of the NHS to its knees in 2017, and which was blamed on North Korea as another example of rogue states threatening the very fabric of society.

The shift away from an international rules-based order alarms her. However, she dismissed the idea that Russia will only step back into line once Vladimir Putin is either forced from office, resigns or dies. 

“They are really precious, these norms,” she said. “And the shift of the last five to 10 years where we have seen some of those eroding is really worrying. 

“It does not require anybody to be dead. Whether that is Putin or former dissidents or anybody else. It requires us to get on with each other and respect each other. 

“It is also in Russia’s interests to have positive relationships with the wider international community.”

Director K added that the beauty of her job was that “from morning to night, I look at where we can do our utmost to prevent harm”.

Russia posed an “acute” threat to the West, she said, while she described the Chinese threat as “chronic”. 

She used an analogy popular in intelligence circles – that Russia is the storm, and China is climate change. “China is absolutely changing the way the world is and that presents amazing opportunities and threats for the UK,” she added.

On the other hand, “Russia is not as influential and has not permeated through every sector of society,” she said.

“Russia blows hot and cold. It has lightning strikes. It can be a bit unpredictable.”

‘Everybody who walks through these doors holds responsibility every day’

Asked how she sleeps at night, given the weight of responsibility on her shoulders, she said: “This is the question we talk about internally and also when I’m with friends – some of whom know what I do and some who don’t. 

“There is a sense that everybody who walks through these doors holds responsibility every day. You don’t know if every single decision you take is world-changing or massively impactful for the UK national security. Every single plot or activity we detect or disrupt can go wrong. We might not intervene at the right moment. There are so many risks that go with this.

“But if you worried about it as you went to bed or think about it as you wake up, it would be unsustainable. It’s not a heroic culture, it’s a very supportive one and that makes a difference.

“So I do wake up worrying about my kids. It is more stuff like that. It’s about how do we actually make a difference? The stuff I genuinely worry about or wake up in the middle of the night is – this is really huge. The state threats, the way the world is changing, exacerbated by Covid. How do we do this properly? This is not within our gift, if it ever was for MI5. It has to be a whole of society effort.

“How do you do that most effectively? That is the stuff at 2am when I come up with another idea of how we might do this.”

She added that there was a “high premium on mental health and access to counselling” in MI5.

“One of the reasons nobody in the media has ever previously interviewed a Director K is we do our work in secret. Necessarily – it’s really sensitive work. But one of the reasons I am talking to you now is we need a whole of society effort. 

“It is not a spy film thing. This affects everybody. In order to help people understand that we [MI5] need to break open a bit more about what we can see and encourage people to think individually about what they can do.”

It is a rallying cry for the 21st century.

Do not be naive about the threat, says Director K

The “ubiquity of the threat”, Director K said, means all of us need to be on our guard. 

She cited the threat of “economic espionage”. There are campaigns already in place, such as “Think Before You Link”, warning academics and business leaders not to let any foreigner link to them on social networking sites.

“We need academia and industry to understand what the threats are and not to be naïve about them,” she implored. “We need them to understand there is a threat from hostile predatory foreign direct economic investment and help them work out what to do about it.

“I look at my kids and they are doing their best at school and have some great opportunities ahead. I am hoping they go into science and a tech-confident UK economy in however many years time. Then I look at how some hostile states are…stealing our IP [intellectual property] for their own advantage and I hope that collectively we can protect that. We need to protect our innovation and our future.”

Britain is leading the world in such new developments as artificial intelligence, quantum physics and machine learning. However, that “also means all of those are open to exploitation and part of that open science relies on trust”, she said. “But we regularly see some states taking advantage of it. We are seeing early stage IP being acquired and then stolen.”

She warned startups against selling stakes to unscrupulous companies based in hostile foreign states. “It could look very attractive to a small, pioneering startup to be attractive to Chinese investment,” Director K said. “But we are seeing all too often that IP being stolen and the benefits do not accrue to the company, and ultimately to our society, our economy.”

Behind the scenes, she admitted, MI5 advises against certain deals being done. The intelligence agency works with the Centre for the Protection of National Infrastructure, a government body accountable to MI5, to advise companies on any ongoing threats.

“It is often not about stopping it but managing it, because ultimately the UK needs investment. Stopping all of this doesn’t help us, it cuts us off. This is about finding the balance… But where we see individual companies or sectors being targeted we will focus our efforts there.”

Pressed on what industries and sectors need to be protected, she said: “Where there is a national security threat from foreign investment, that is where we focus our interest. MI5 is able to focus on the harder end of the threat. MI5 should not be – and isn’t – the economic policeman of the UK.”

The National Security and Investment Act, which comes into force in January, will give the Government the power to unwind or block any acquisition deemed to be a threat to national security. The new legislation will underpin much of MI5’s ongoing work.

The attempts to steal the Covid vaccine developed at Oxford University and MI5’s role in investigating that and trying to thwart has added to Director K’s workload. 

“The Covid vaccine is arguably the most valuable discovery probably in our lifetimes and, of course, states are going to compete to either retain or gain an advantage in that competition,” she said. 

“I think the vaccine also showed some of the misinformation campaigns other states were prepared to launch in the UK. We know the really malign states directed aspects of that.

“Any country with the ability to launch state-backed acquisition campaigns with an interest in the vaccine and large population to protect would have been interested and I don’t think it is exclusively Russia.”

Another burning issue has been allegations of “malign interference” in elections and in the referendum by Russia. Director K has faith in the British electorate. “Luckily, the UK public is more discerning and more thoughtful about their sources of information than looking for alternatives,” she said.

Director K makes an impassioned plea for a modernised Official Secrets Act, which is currently being revamped amid complaints from the espionage community that it is 100 years old and out of date. 

“At the moment it is not illegal to be a foreign spy in the UK. That is staggering,” she said. “If we catch somebody with a hand-drawn map intending to send it to an enemy, then we have the legislation. We have only used it twice [successfully] in the last 10 years because of that.”

A Russian spy caught working in the British Embassy in Berlin may well be the third.

‘We collectively need to be much more resilient’

Director K has been at MI5 for two years, having transferred to the domestic agency after two decades with MI6. She spent at least some of that time in hostile, dangerous territory. 

“I started life as an MI6 agent runner and spent most of my career overseas and joined MI5 to do this job,” she said.

Before that, she had studied anthropology because she was “really fascinated by human behaviour and how and why people act”. 

Anthropology, she explained, “is really useful for this job because it isn’t really about states doing this to each other. It is individuals who do this”. 

She added: “Our adversaries are people and the victims are people and it is really important to see it on that level. 

“I have lived in countries throughout my career where democratic principles and freedoms sometimes disappear overnight, or a free press squashed, and it makes you realise quite how special the UK is. It is really rare and really worth protecting.

“So what I worry about for my kids is not the day to day threat, the theft of IP or even frankly an individual assassination plot. But it is the change you can feel in the way global geopolitics is playing out in our society right now. It is quite hard to convey that to the public without being alarmist. But this is different. That is why we collectively need to be much more resilient.”

Talk of the children turns to their cunning discovery that mum’s workplace was not among civil servants in some anodyne government department – as Director K must tell her friends – but in the bowels of Thames House, the headquarters of MI5, not far from the Palace of Westminster.