Original subtitles

DRAMATIC MUSIC

This city that we are conducting this interview in

is without doubt the epicentre of espionage.

Without doubt.

London belonged to me. I would say so.

I don't know any intelligence officer

who did like London.

London has been seen as a focal point

for lots of foreign spies.

Spies are drawn to cities

where there is power and there is influence.

Most major cities are spy hubs.

London certainly has that reputation,

has had for many years, because of the intersection

between US interests, European interests, and, of course,

Russian interest as well.

Foreign conflicts sometimes come in to London

because of its international nature, because you have dissidents here,

you have other countries trying to target defectors

and people here.

And so you do have this enormous array of killing.

Espionage is an invisible art,

and usually, we don't want to be noticed.

We blend in and work in the shadows.

Our job is to steal secrets and not get caught.

To a large extent, assassinations really have no place

in the work of spies.

You're trying to get secrets from people. You want them to be alive.

You definitely see other countries

using assassination and targeted killings

as a tool, almost an everyday tool.

The Russian and Soviet state has a murky tradition

of killing people that it regards as enemies.

Now, that could be Ukrainian fascists,

it could be traitors within Moscow's own spy services.

It could be enemies like Trotsky...

..felled with an ice pick in the head

by an agent sent by Stalin.

And others are more, kind of, "question mark", you might say.

If you're a traitor, in their eyes, there is only one penalty,

and that's death.

And it appears

death by as obvious and painful a method as possible.

BIG BEN CHIMES

NEWSREADER: It really is like the Cold War.

Police in full chemical suits

on the streets of Salisbury

and a Russian double agent who worked for MI6

feared poisoned and critically ill.

Sergei Skripal was a former officer in the GRU,

which is the Russian's First Directorate,

their oldest military intelligence organisation.

They are the tough guys.

They are the intelligence soldiers within the Russian military.

They're people who are trained to go abroad,

to collect secrets,

but also, potentially, to carry out covert military operations overseas.

So Sergei Skripal joins the GRU.

He's an undercover intelligence officer,

he's posted abroad in embassies.

In some cases tried to collect intelligence, effectively.

And it's while he's in Spain, at the embassy there,

that he's approached by someone

who initially looks like a businessman,

asking if he wants to do deals, do some consultancy.

But eventually that turns into a relationship with MI6,

as he's recruited as an agent by British intelligence

to act as a spy in the mid-1990s.

He was, to the Russians, a traitor to the Russian nation.

And Vladimir Putin has stood up and said, publicly,

that traitors should be killed.

It looks like Sergei Skripal could have betrayed the identities

of hundreds of undercover Russian intelligence officers,

GRU officers,

serving in Europe and around the world, to MI6.

They're not interested in Skripal at all.

They never was interested.

Hence, well, there's enough traitors in my own agency.

Of course, he knew a lot

about the officers of our military intelligence,

and I'm sure he spoiled their careers.

Then finally, in the noughties, his luck ran out.

By this point, Vladimir Putin was in power as president

and there was a kind of chill in the air.

Skripal was demonstratively arrested.

He wasn't just arrested, he was arrested with TV cameras...

..dragged out.

So, Skripal is in prison. 13-year prison sentence.

No prospect of release.

And then something incredible happens.

In July 2010,

Skripal was added to the list of exchangees

in the spy swap that was conducted in Vienna,

where ten Russian illegals

who had been arrested in the United States...

..were released in return for four Russians.

And so you get an old-fashioned, almost Cold War-like spy swap

at Vienna airport,

in which Russians arrested in America

are swapped for Russians who'd been spying for the West,

serving time in Russian prisons. And one of those is Sergei Skripal.

He was brought back into the UK

and then settled into Salisbury after he got debriefed.

He was mostly working in consultant capacity,

delivering, lecturing, et cetera, et cetera, et cetera.

Oh, it formally could be considered as work.

But he was delivering no damage to Russia.

To the Russians, it doesn't matter.

It does not matter.

NEWSREEL: As the search continues tonight, so the questions mount.

Were these two people deliberately poisoned?

If so, by who and why?

And has the past of a man disowned by his state

led to him becoming critically ill?

The problem was simply GRU was told to do it,

they came up with a plan,

then they sent the plan for authorisation.

It was authorised and they went ahead.

So the GRU is quite a big, sprawling outfit,

and within it, located outside the GRU's main building,

in a facility in north-west Moscow,

is a sort of diversionary group of war veterans, combat veterans,

who perform special tasks.

Such as sabotage, such as murder,

such as assassination on behalf of the state.

I can't exclude even the situation

when the people whose career he's spoiled

decided to make revenge on him

and went independently there to London, you see, to kill him.

You see, it's crazy situation now.

Two intelligence officers working for the GRU,

Petrov and Boshirov, but that's their cover names,

had flown in to London on a direct flight...

..book into an inconspicuous hotel in the East End,

and on Saturday, travelled by train to Salisbury,

on what, clearly, we now know as a reconnaissance exercise.

Petrov and Boshirov go to Salisbury,

and they are seen and captured on CCTV, it turns out,

wandering round the streets,

and going towards the vicinity of Sergei Skripal's house.

And that their real names were Chepiga and Mishkin...

..and we know that they were basically soldiers

and they were part of a super secret diversionary group...

..based in France, near the Swiss border,

who had been behind all sorts of murders or attempted murders,

assassinations.

NEWSREADER: Walking, apparently without concern,

it's believed this fleeting CCTV video

shows Sergei Skripal and daughter Yulia

heading towards a park in Salisbury,

the poison possibly already coursing through their bodies.

The Russians, the Soviets, always want fearsome control

over politics and political expression inside their own country.

The threat to that is the exile.

The threat to that of people who are operating outside their space,

the answer to that problem is assassination.

RADIO NEWSREEL: 12 hours, Greenwich Mean Time.

RADIO NEWSREEL: BBC World Service presents Radio Newsreel.

RADIO NEWSREEL: BBC World Service broadcasting worldwide.

SPEAKS IN BULGARIAN

Georgi Markov is often described, I think, as a dissident.

He's an incredibly brilliant writer and because of his talent,

he shot to the top of Bulgarian literary life.

It was in the early '70s that he arrived in the UK.

Markov is working for the BBC's overseas service,

broadcasting anti-Communist propaganda into Eastern Europe.

SPEAKS IN BULGARIAN

MARKOV: I feel in myself a necessity to rebel

against any kind of authorities.

The theme that he spoke on in these broadcasts

was the corruption and the lack of credibility

and the closed-mindedness of the regime.

And the lies that they told, not just to the people,

but sort of about themselves.

We know that the Bulgarian intelligence services

wanted Markov dead. They wanted him dead for a long time.

He was a prominent critic of the regime.

I always had a feeling that he is looking over his shoulder.

He told me that he gets threatening phone calls

and I saw the copy of a court decision

that he is sentenced to death for being an enemy to the state.

So on the 7th September 1978,

it's another working day for Markov in the BBC World Service.

He does what he always does.

He drives his car a certain way into London,

then he catches a bus from Waterloo Bridge.

Markov did what he did more or less every day.

He parked his car and then he went up the steps,

and at the top of the steps on Waterloo Bridge, there's a bus stop.

Waiting there for the bus, in the queue,

and behind him is what he thinks of

as a normal British businessman, city type.

Someone in a raincoat with an umbrella.

That person stumbles

and the umbrella jabs him in the back of the leg.

He feels a little prick. It's like a bee sting.

And he turns around and there was a man

who appeared to have dropped an umbrella,

who apologised to him and moved on. He didn't think anything more of it.

But as the day went on, quite quickly,

he started to feel extremely ill indeed.

I met him when he came back with the bulletin in his hand.

He was going to the studio,

grey in the face, and walking not very...

I immediately assumed that he's drunk.

And when passing, I noticed that his eyes,

they were... how shall I put it?

Not here. He didn't look straight.

I said something, "Are you going all right?" Or something.

And he waved me off. "Get lost."

And that's it. That was the last time I saw him.

He starts to have flu-like symptoms, a temperature,

and then he realises this is potentially an attack.

He reports to hospital

and initially, the doctors are quite dismissive.

He was telling them that he'd been attacked,

but the only evidence of that

was this little sort of red pimple on the back of his leg.

They think it's just an infection.

They're treating him for standard infections,

but within two days,

they realise the infection is overwhelming his body.

He basically suffered organ failure...

..and by 11th September, he was dead.

When an autopsy is conducted,

the doctors eventually find a tiny metal ball.

Smaller than you would find in the tip of a biro.

When they look at it, they see there are two holes in it.

Tiny, tiny holes.

What they found was a pellet full of ricin,

which had been unleashed, somehow, from this umbrella into his leg.

Ricin is a biological toxin which is incredibly virulent,

very toxic, and it's made from castor beans.

That ricin would have killed him, you know, very, very quickly.

It is incredibly toxic.

It's never been definitively proved who did it.

The police have looked at this over the years to try and understand it.

All the evidence seems to point to Bulgarian intelligence

having been behind the operation, but with the support of the KGB,

who provided some of that equipment to carry out the assassination.

The General Secretary of the Bulgarian party, Zhivkov,

appealed to Mr Brezhnev to help him to liquidate Markov,

and the only thing which we could do

is to provide them with this umbrella,

which was specially made, invented.

No-one had heard of a weaponised umbrella before this happened.

The special department which was in charge

of creating these types of technologies for killing

had, in fact, developed some kind of umbrella gun

that was suddenly capable of firing a pellet of this sort.

I mean, it is very James Bond-ish, you know,

the idea that the QC, the Q Branch in the Soviet Union,

is developing these weapons.

And this has since become

the archetypal Cold War assassination.

It's really hit the public imagination

because it's got hitmen, it's got gadgetry, it's got poison.

And it also caught public imagination

because, not only was it a crazy, ingenious assassination method,

it happened right in the centre of London.

NEWSREADER 1: This story of spies and counterespionage

turned from claim to counter-claim today.

A leading toxicologist suggested... NEWSREADER: Alexander Litvinenko,

a former lieutenant colonel in the Russian Federal Security Service,

or FSB...

NEWSREADER: Tonight, this former Russian agent is in hospital.

His life hangs in the balance.

I met my husband, Sasha, in 1993,

just a few years after Soviet Union collapsed.

And of course it was mess,

but it was a lot of hope for new Russia.

In 2006, I was the head of the anti-terrorist branch

at Scotland Yard.

I remember very well the first time

I ever heard the name Alexander Litvinenko.

I was sitting in my office on the 15th floor

of what was then Scotland Yard.

One of my colleagues came in and said that in hospital,

in north London, was a man who said that he was a former KGB officer

and that he had been poisoned

by some of his former colleagues in London.

Alexander Litvinenko is a fascinating character.

Essentially, he was a sort of cop.

He was a detective who specialised in going after

organised crime groups in the 1990s.

And he was a sort of decent, honest, hardworking officer.

Every time when he tried to investigate cases

linked to organised crime,

it all came back to very high-rank officers of FSB

or people from Russian Parliament.

And it was always cut.

It means he was not allowed to complete this investigation.

It's something which is beyond my understanding, you know?

To care about Litvinenko, some Lieutenant Colonel.

It's a very minor person, you know, to care about.

I don't think that Mr Putin even knew about such a little person

as Mr Litvinenko.

DRAMATIC MUSIC

Alexander Litvinenko, he'd actually confronted Putin himself

in the late '90s, when Putin had become the head of the FSB,

the Russian security service.

Alexander Litvinenko had gone to him to say

that he believed that there was corruption, assassination,

dark dealings going on with the FSB.

TRANSLATOR: I gave him my report and he looked at the charge,

but refused to take it. He also asked for my home phone number.

I ask him what it was for.

He said, "I'll call you." A few days later, an FSB friend laughed at me.

And he said, "Putin ordered us to bug your phone."

Pretty quickly after this, Litvinenko, he's in prison.

He's released, he's rearrested, he's in prison again,

and it's clear that Putin wants to get rid of Litvinenko forever.

TRANSLATOR: I left Russia because I was in fear for my life

and afraid for the safety of my family and my six-year-old son.

If I go back to Russia, I won't last long there.

I won't live long. I was told that I had betrayed the system.

And that the Federal Security Service does not forgive traitors.

Putin views Litvinenko as a traitor for having gone to him

and having turned against his colleagues in the FSB.

So from that moment on, really,

Putin and Litvinenko themselves are personal enemies.

They come to have an intense dislike for each other.

And when it comes to matters of life and death,

when it comes to sensitive international assassinations,

operations abroad, only Putin can decide this.

NEWSREADER: It was Litvinenko's investigation into the murder

of this woman that could have made him a target this time.

His friend, the Russian journalist Anna Politkovskaya,

was murdered in her apartment block in October.

She, too, was a harsh critic of the Russian president.

Anna Politkovskaya, Sasha's friend.

She was, Sasha believed, in the list of enemies of Russia state.

My name is Alexander Litvinenko. I'm former KGB and FSB officer.

My speech is difficult for me. Can I use translator?

Somebody has asked you directly, "Who is guilty of Anna's death?

"Who has killed her?"

ALEXANDER REPLIES IN RUSSIAN

TRANSLATOR: And I can directly answer you.

It is Mr Putin, the president of the Russian Federation,

who has killed her.

When Anna was assassinated, he was really shocked.

And all this discussion about these names

and this list of assassinated of, like, one by one.

And everybody said, "It's not true." But when it happened,

Sasha realised it's true.

Sasha knew he on this list, but he believed he's a professional

and good enough to recognise a danger.

And one version... This is not verified.

But one version of what happened

is that Putin meets with his spy chiefs at some point in 2006,

and turns to them, "I never want to hear that man's name again. Ever."

And that's clear. The order is kill Litvinenko.

NEWSREADER: If there was any doubt

Litvinenko was a target of the Kremlin,

you need only watch this video of Russian Special Forces in training.

Their target - Alexander Litvinenko.

CORERA: Andrey Lugovoy and Dmitry Kovtun

are both former Russian security service officers

who appear to have left the employ of the Russian security services

and are involved in this world of investigations,

which Alexander Litvinenko was also involved in.

Lugovoy was the first person who need to approach Sasha.

He was not a friend, but he was man from this circle.

And then they started to discuss to do business together.

Again, it's all look natural.

But instead, what they don't realise is that Lugovoy is still

effectively working on behalf of the Russian security service,

the FSB, who use him to target Litvinenko.

Dmitry Kovtun is a very strange, weird character in this story.

I mean, he essentially served in the Soviet military,

came from a Soviet military family,

which is where he got to know Andre Lugovoy.

I remember Sasha was immediately unpleasant of Kovtun.

He even couldn't say exactly what is his name.

He said, he's a... like a mystery man.

It very quickly became apparent that Lugovoy and Kovtun

were two people that we needed to take a particular interest in.

Alexander Litvinenko, 1st of November 2006,

it was a, sort of, regular day for him.

I mean, he was living in Muswell Hill, in north London,

with his wife, Marina, and their son Anatoly.

There was a business meeting planned with Andrey Lugovoy.

CCTV tracks him. You can see these images of him

walking through central London.

And he gets to the Millennium Hotel in Grosvenor Square

just ahead of a 4pm appointment. And actually, you look at the CCTV

and it's rather poignant, you see him arriving in the lobby,

making a call, telling Lugovoy he's there.

We see Lugovoy and Kovtun captured on camera,

including in the hotel itself, in the Millennium Hotel.

At about 3.30pm, there's video of Lugovoy going up the steps,

turning left into the gents' toilets,

one of his hands is kind of tucked in like this,

and he's got this kind of grey, fell visage.

A few minutes after that, Dmitry Kovtun does the same thing,

repeats the journey, goes into the gents' toilets.

And it looks like they were hatching the plot.

There is an interesting thing which is the sort of sense that Russia,

that they are geniuses, they all play chess,

they know things, they're wizards.

And that most certainly applies

to their attributes within the secret world.

But they make mistakes. Trust me. They do make mistakes.

When Sasha came to this meeting, he was asked,

"Would you like to drink anything?"

And some alcohol was served and Sasha said,

"You know I don't drink alcohol."

He said, "OK, but you could drink tea?"

Tea was already prepared.

There's a pot of tea, a white ceramic pot already on the table.

Lugovoy calls over the waiter, who brings a fresh cup,

and suggests to Litvinenko that he has some tea.

And when he took sip of this tea, he was... immediately realised

something wrong.

There was something wrong with the tea,

something strange about the tea. And he leaves it.

He didn't finish this cup. Maybe few sips.

Maybe what helps him to survive for some longer period.

But after that moment, couple of sips,

actually, there's nothing that could be done to save Litvinenko.

That evening, Litvinenko starts to feel ill.

He's vomiting, he's feeling sick. He calls his wife Marina for help.

He couldn't breathe properly.

And he always asked to open the window for fresh air.

But in the second day at home, he started bleeding.

Sasha lost weight, he looked very weak.

It was very difficult for him to walk from upstairs to downstairs.

And he knows, even though it takes a little while

for others to kind of realise this,

he knows that he's been poisoned and he tells Marina,

"I think I've been poisoned."

Eventually, he is admitted to hospital,

and eventually moved to UCL,

where the police come and visit him and hear his story.

We dispatched an officer to interview Alexander Litvinenko

in hospital. It was most unusual because we had, in effect,

what was a living murder victim, someone who was describing...

And I think he was pretty clear in his own mind

that he might well not survive this illness.

But he was able to give a description

of what had happened to him.

For such action requires the highest level of authorisation

because anybody who worked in the KGB knows it.

The system remains the same.

These operations have always been very centralised.

It was an agenda in which Putin was brought up.

Exactly which was everything must be authorised.

The message was loud and clear from Russia.

"This is what can happen to you as well if you do what he's done."

The Russian state is ruthless in tracking down what it perceives

to be its traitors, people who were part of the regime, who worked there

and who left and joined the other side.

The message that it sends back to members of the Russian services,

"If you betray, your end is going to be agonising."

There have definitely been examples when the British government

has talked a lot about assassination,

and to some extent, done planning for assassination.

I once asked an MI6 chief directly, do you have a license to kill?

He said, "No, we don't have a license to kill."

And I then asked him, "Did MI6 ever have a license to kill?"

And there was a little pause before he gave a more equivocal answer.

And I think what that tells you is that in the past,

MI6 has been involved in assassination plots.

NEWSREEL: Our quarrel is not with Egypt,

still less with the Arab world. It is with Colonel Nasser.

SHUTTER CLICK

There is some talk about assassination

in the Middle East in the 1950s.

And this is particularly aimed at the leader of Egypt,

Gamal Abdel Nasser.

Instead of meeting us with friendship,

Colonel Nasser conducted a vicious propaganda campaign

against our country. He has shown that he is not a man

who can be trusted to keep an agreement.

Nasser is dedicated to Arab nationalism

and throwing British bases and British interests

out of the Middle East, right across the region.

This is what makes Eden see red.

Eden took it very personally and he wanted Nasser removed.

He wanted him overthrown. He authorised

a load of different covert operations to get rid of Nasser.

You have two different British foreign policies in '56.

You have the one that you'll read about in the newspapers.

And then you have the second foreign policy, which is in the shadows.

Which is all the planning of, "How do we assassinate Nasser?

"When do we do it? Where do we do it?"

Not only did Anthony Eden want Nasser dead,

he was also very open about this.

Anthony Nutting, who is the foreign office permanent secretary,

he is phoned by Eden on an open line, which is incredibly unusual.

Nutting, now off duty, at the Savoy,

"What's all this about neutralising Nasser? What's all this?

"I don't want Nasser neutralised. I want him murdered."

"I want him destroyed. Don't you understand?"

"I don't want any messing around. He has to go."

Eden charged MI6 with coming up with ideas to kill Nasser.

George Kennedy Young, who was a deputy head of MI6,

was certainly a man who was not shy

of issues like coups and assassinations.

Eden basically gives him carte blanche that,

"You go ahead and do it, organise it,

"and you are reporting directly to me."

George Young was also quite open about these plans.

He insisted that Eden had given him personal instruction

to bump Nasser off.

The Foreign Office are horrified by this.

Later, the dispute also becomes known as "the horrors".

But George Young is gung-ho for it and he starts to organise this.

MI6 has an entire department,

and it's public knowledge that it's called the Q department.

And they do make weird, wacky gadgets. That is true.

And they are ingenious.

All intelligence services have something like a Q branch

because there is technical intelligence.

You do need these things. And these branches have indeed

developed well-known assassination weapons.

Famously, Fleming's character, Q, the gadget man,

is actually an inspiration of two characters

who worked for a branch of military intelligence, MI9.

In the 1950s, Frank Quinn is the MI6 technical officer.

He's absolutely the equivalent of Q in James Bond,

and not just designing assassination weapons,

but also all the covert paraphernalia of spying.

X-ray document scanner.

A pen. This is a class IV grenade.

Three clicks arms the four-second fuse.

Another three disarms it.

How long did you say the fuse was?

Oh, grow up, 007.

People in London are playing around with how you assassinate Nasser.

Do you poison him? Do you shoot him?

Quinn developed the idea of an exploding Remington razor.

This was packed with plastic explosive.

Nasser was known to use this particular razor

and he was known to take regular shavings.

They developed a packet of cigarettes which had the capability

of firing a poisoned dart.

And apparently, this poisoned dart was tested on a poor sheep

down at Porton Down. And let's just say it worked.

Now, one that Frank Quinn we know was definitely involved in

was putting poison in Nasser's favourite chocolates.

He had a particular brand of chocolates he liked,

and Quinn ordered various boxes of them.

Poisoning Nasser using chocolates was very difficult to achieve

because MI6's technicians in Q branch

had to work out how you can take the bottom off of a chocolate,

insert poison into it, and then replace the bottom of the chocolate

without anyone knowing that it had been tampered with.

Q branch develops, effectively, the way it's going to be delivered.

This does make it to Cairo through a diplomatic pouch.

But now it's sitting in your embassy in Cairo.

You've got to get them to Nasser.

MI6 had a problem with their plans to assassinate Nasser

in that their officers were no longer in Egypt,

they'd been kicked out by Nasser.

The British didn't have access to Nasser.

They couldn't get the poison dart to Nasser.

They couldn't get the chocolates to Nasser.

As far as we know, this was the last time

that a British serving prime minister attempted an assassination.

Britain is bungling and amateur.

That's one of the reasons that Nasser lived such a long life.

At one point, they were going to pay Nasser's doctor the equivalent

of half a million pounds in today's money to kill Nasser.

And... he took the money and ran.

MUSIC: 'JAMES BOND THEME' by Monty Norman

A license to kill for MI6, it doesn't exist.

Assassinations may have once been authorised

by the British government,

but in modern times,

it's purely the preserve of spy fiction.

By nature of what you're doing,

you're breaking that other country's laws.

So whipping out a so-called license to kill

isn't gonna save your bacon.

The concepts of license to kill

emerge through the exploits of James Bond,

the most famous of the fictional intelligence officers.

He goes around the world shooting people, blowing things up,

sleeping with people, doing whatever he wants.

What do you say to that?

HE SIGHS It's a waste of good Scotch.

The idea of a license to kill comes from the world of James Bond

and doesn't have any place in reality.

People aren't being bumped off. It just simply isn't that way.

You don't really want to be carrying a gun. The old James Bond myth -

trained to kill, carrying a Walther PPK, you know,

around all the time. It's just that, it's a myth.

We can't get enough of the stories, whether they're the real history

from declassified files or whether they're from the pen

of the likes of John le Carre or Frederick Forsyth.

This man is supposed to be a secret agent.

He walks into a room and they say "Good evening, Mr Bond,

"we have been expecting you." That's a secret agent?

I mean, the mission's blown.

Assassination is not something that British ministers would sanction.

And there is no double-0 section in MI6 that goes around

killing the Queen's enemies.

NEWSREADER: Tuesday afternoon in Salisbury last week.

The scene could hardly be any more mundane,

except this is Sergei Skripal,

the former spy

who would be specifically targeted with his daughter days later.

Everything is normal in Salisbury until it isn't normal.

So essentially, Sergei Skripal is there.

His daughter Yulia is flying over from Moscow.

I was at a birthday party and while I was there,

I had an email from my news editor at the time saying that

someone had let us know that the air ambulance had landed

in Salisbury city centre.

RUSSIAN ACCENT: We got Chepiga and Mishkin coming down to Salisbury

to go and look at the very tall spire in Salisbury Cathedral,

because it is spectacular. Excuse my Russian accent.

We could see, from the CCTV, them arriving.

The, sort of, most shocking pictures, I think,

for people in Salisbury, was seeing them arriving

at the train station and... and walking around the city centre.

They are seen and captured on CCTV, it turns out,

wandering round the streets

and going towards the vicinity of Sergei Skripal's house.

They go to Skripal's house, middle of the day,

no-one around, and they apply Novichok, a lethal nerve agent,

to his front door handle.

Sergei Skripal, he then comes into contact with that on the Sunday,

and then he and his daughter, Yulia, fall seriously ill.

Yulia collapses

and Sergei starts muttering and behaving strangely,

and passersby begin to notice them and think, you know,

"Maybe they're off on drugs or something."

When I arrived in the Maltings, it was late afternoon.

The two people were found on a bench, which was over there,

and which has now been removed.

It would have been a couple of hours, I think, after that,

that the fire crews turned up.

And that was when it first became obvious

that something more unusual was happening.

I came into work as usual on the Monday.

I did some activity in theatres,

but I'd heard rumours that something was going on.

I was in Abu Dhabi at the time, giving a talk to people about

chemical and biological terror and state terror attacks.

I got out and I had hundreds of missed calls and WhatsApp messages

and everything else.

We had two patients admitted with a working diagnosis

of opioid poisoning.

These patients required intensive care.

When I got to meet and examine the patients,

things didn't sit right with me

that that was actually what was going on.

And by that stage also, we'd come to be aware of the identity

and professional background of our patients.

And so there were alarm bells ringing about whether

this could've been some nefarious activity and a targeted incident.

When I went into work on the Tuesday morning,

I took handover from my registrar who'd been on overnight,

who just recently received a phone call

from the chief medical officer at Porton Down,

explaining that our patients had had severe poisoning

with an anticholinesterase toxin,

which is a very, very serious and life-threatening condition,

where patients can go into multi-organ failure.

The symptoms that are being presented in hospital in Salisbury

are consistent with a nerve agent poison.

I think the first time that we heard that it definitely was a nerve agent

would've been when it came from the House of Commons.

NEWSREADER: It is now clear that Mr Skripal and his daughter

were poisoned with a military-grade nerve agent

of a type developed by Russia.

This is part of a group of nerve agents known as Novichok.

The government has concluded that it is highly likely

that Russia was responsible

for the act against Sergei and Yulia Skripal.

Novichok is a lethal nerve agent,

which was created in secret facilities in Sarov in Russia,

in the 1970s and 1980s by an elite group of scientists

working for the state.

It's probably the most deadly manmade chemical ever produced.

To try and put it in toxicity terms, say something like chlorine,

you know, the first chemical weapon, is toxicity one,

the first nerve agent, Sarin, developed by the Nazis

before the Second World War would be 5,000.

Novichok would be about 60 or 70,000.

There was enough Novichok there to kill everybody in Salisbury.

You could have killed tens, if not hundreds of thousands, of people.

To use a nerve agent on the streets of Britain

was something that no-one expected and no-one had ever seen before.

Novichok is basically a calling card.

Really, only Russia produces it. It's linked with the Russian state.

It was used in Salisbury

by a Russian state military intelligence outfit.

All of the signs point back to Russia.

Novichok is produced only in Russia.

And so, it's as if Putin has left his visit card.

It was Putin's visit card.

NEWSREADER: The mystery surrounding Alexander Litvinenko's death

is more and more complex. But the grief of a family

is easy to understand. His widow, Marina, has lost a husband.

Their 12-year-old son has lost his dad.

I believe till last moment, he would recover.

Before Sasha died, night before that, it was cardio arrest

and he'd been unconscious last day.

He'd been all under support machines.

And I believe his heart was so strong,

and he would be able to stay longer, even this... this support machine.

But his heart stopped at the end.

The day that he died, he died about 9pm in the evening.

But that afternoon, Aldermaston, the government scientific facility,

came back with a result

from an examination of his urine and his blood.

I was on the motorway on my way back to London

when I received a phone call to say that, er, the substance

with which Litvinenko had been poisoned had been identified,

and it was something called Polonium 210.

Polonium 210 is a radiological isotope, very, very rare,

that is used in the nuclear weapons industry.

Very, very few people have it.

Any chemical or biological, radiological weapon

would have to be authorised at the highest level.

ANNOUNCER: Vladimir Vladimirovich Putin!

This is not something that, you know, any random person or criminal

or someone else could get hold of, polonium.

This has to come through a state.

And at this point, it became clear to the British Government

that this was not just a suspicious death or a killing.

What they were dealing with was a major and unprecedented crisis.

Very quickly, the police are able to understand that Dmitry Kovtun

and Andrey Lugovoy are key suspects in this.

They can see from the fact they've met Litvinenko,

from the times of when he was poisoned,

then they're able to put together the trail of polonium

and match even to the aircraft they travelled on to the UK,

as well as other places they'd been to in London.

Wherever they went, there was a kind of ghostly trail of particles,

of gamma particles, which were subsequently detected.

And that means that this assassination can be reconstructed

in minute detail, minute by minute, hour by hour.

We tracked their movements. We found where they'd stayed in London.

We found which aircraft they'd used to fly in and out of the country on,

we found the offices that they'd visited in London.

There were over 40 sites

of radioactive contamination across London.

Here you've got the weapon

that they've left all over the place,

but which helped immensely in terms of putting together the jigsaw.

If the British security services

and police hadn't worked out what it was,

this death may have just gone down as a mystery.

If Sasha died before he was able to give this evidence -

and people who committed this crime,

they exactly wanted him to die before -

again, it would be just unexplained death and not any trace of Polonium,

not any links to Russia,

not any links to these people who did this crime.

APPLAUSE

If you listen to the language Vladimir Putin uses in,

for instance, press conferences and interviews,

when he's asked about people who betrayed Russia, it is remarkable.

He talks about swine, traitors.

And it's quite clear that he is signalling they deserve to die.

Putin's approach to assassination is fascinating.

If we go back to the mid-20th century, quite often,

the objective was to kill someone in a way that was hidden

or at least plausibly deniable.

What we see with Putin is a shift to implausible deniability.

It was a message first and foremost to the British Government

and to MI6. It says that, "We've got no respect for you.

"We can pursue our traitors at a time of our choosing,

"and we can settle with them. We can snuff them out whenever we want,

"and you are weak, you are powerless,

"and we can humiliate you."

The murders, the murky killings continue.

The idea that foreign assassins can come into London and kill someone

is an embarrassing failure.

It suggests that people, including defectors,

are not safe in Britain. And that is something

which worries and embarrasses the security services

and the police when it does happen.

If you look around the world, you can see that there certainly are

intelligence agencies that do use assassinations.

This is not something the UK does.

In most countries in the world, espionage is deemed illegal.

So here we are, people like me, going over there,

breaking other country's laws.

That's the nature of the job. We're spies. That's what we do.

I'm not sure it comes from a higher sense of morality,

but rather this - that if you can get to somebody to assassinate them,

you can get to them to bug them, to recruit them, to undermine them.

Assassination is something that any service could do,

but doesn't necessarily have to do.

I am quite sure I am in the list of these legitimate targets.

Vladimir Putin would definitely not hesitate to give authorisation.

How successful it would be, we'll never know.

Whether they manage to do so or not, we'll never know.

The idea of compromise.

Thinking, to a certain level,

it's not about winning someone round, it's about coercion.

Which is nasty.

Vassall is essentially compromised

by being invited to a KGB-organised orgy.

Sex between two consenting adults

is surely a better way to extract intelligence than torture.

Subtitles by accessibility@itv.com