Original subtitles

ROHIT KACHROO: Early morning, London.

At Britain's busiest airport, journeys are just beginning.

MAN 1: This is an almost unimaginable plot.

Seven flights bound for North America.

The United Kingdom would've been used

as a launch pad to attack America.

Among the thousands boarding, seven dangerous men,

all of them British.

These were professionals.

This was a cell that had training.

They slip through security carrying lethal devices.

You've got your drink bottle. You've got your camera.

You can then wire those together.

You have created an effective bomb.

MAN 2: They were clearly going to go through this.

When can we take it down?

Are they on the brink?

And somewhere over the Atlantic, passenger planes go down.

What you've just watched is what could have happened...

..had the liquid bomb plot not been foiled.

But this was the plan, and the intentions were real.

NEWSREEL: At altitude, this would lead to the plane disintegrating.

We would not have recovered fully from this.

You would've had, probably, a death toll higher than 9/11.

I think you might not have civil aviation now.

Twenty years on, this is the story of how close the plotters came...

..and of the British man said to be at the heart of it.

This extraordinary journey.

He is seen as something of Al-Qaeda's point man.

And of the suspected explosives expert who walked free.

MAN: He had a degree of supervision.

When the way we travel was changed in an instant.

Those queues stretch right the way around the airport.

Would this have been the point where people would've started to say,

"No, I'm not going to fly"?

EXPLOSION

Speaking for the first time,

we will hear from spies on both sides of the Atlantic

who helped to foil this massive plot.

DISGUISED VOICE: And, obviously, there's a potential consequence

of not just fucking up an operation but being hurt.

The biggest surveillance operation in British history...

..and a worldwide race to intercept what would have been

one of the most devastating terror attacks of all time.

There would have been a terrible, tragic loss of life.

The government would've been in grave danger of falling.

A spring morning in 2002.

As dawn breaks in Alum Rock, a suburb of Birmingham,

news begins to spread.

Overnight, a local resident was murdered.

He was attacked in the street and suffered close to 30 stab wounds.

His heart probably stopped bleeding

before the attackers stopped stabbing him.

He died on the doorstep of his home.

This was multiple, frenzied, purposeful.

The intent was clear.

Whoever attacked him wanted him,

or the person they thought they were attacking, dead.

The victim was Mohammed Saeed, a father of two,

a delivery driver who'd just finished his night shift.

Andy Hough was one of the first senior officers on the scene.

I suspect that there were only a few people

that knew what really happened

and, more importantly, why it happened.

However, I do know that they eventually identified a suspect.

But this didn't appear to be a random killing

because the man wanted for questioning

was, in fact, Saeed's nephew, 21-year-old Rashid Rauf.

He left the country not long after the murder...

..and went to Pakistan.

And Rauf didn't leave alone.

One of his friends from his university days left with him, too,

20-year-old Mohammed Yasar Gulzar.

It's an unsolved murder, and police try to find Rauf.

It just turned out that he had vanished.

He's effectively forced by circumstances

to flee to Pakistan because he is wanted by the police.

We can see that that moment was pivotal.

You know, if he'd stayed in this country,

life might have been very different.

The Pakistani Kashmiri Muslim communities in Birmingham

are close-knit.

They're devout. Strongly attached to religion.

There's always been a strong interest in the Kashmiri cause

and the idea of liberation and independence

from both India and Pakistan.

And, unfortunately, for a tiny fringe,

that translates into support

for the terrorist groups, or jihadi groups, in Kashmir,

seen as resistance fighters.

The area where Rauf grew up is home

to one of Britain's longest-standing Pakistani communities.

Rashid Rauf's own family

is understood to have been deeply devout,

with close links to the local mosque.

Rauf seemed like a very normal person.

He made friends, went to school, played cricket,

and then he went to university for about a year.

And then at some point, he dropped out.

The murder is never solved. The motives remained unclear.

When you are stabbing somebody,

you're looking them in the eye, and they're looking you in the eye.

You've got to be a pretty perverse individual

with no respect for life.

What had looked like a domestic dispute

was, in fact, a step towards Rauf

becoming one of the most dangerous terrorists in the world.

SHOUTING, COMMOTION

USAMA HASAN: The single most important event

for British Muslims was 9/11...

..and then the war on terror after that.

We will make no distinction

between the terrorists who committed these acts

and those who harbour them.

We have to take action against the whole machinery of mass terrorism.

The early 2000s were a great period of ferment,

defined, I think, in the Muslim world

and amongst some Muslim men,

by a great sense of grievance against Western powers.

This drew a lot of people into the arms of Al-Qaeda

because they had a charismatic leader in Osama bin Laden.

You have this radical, extremist ideology of Al-Qaeda

which says, "This is a war against Islam,

"and it is us against them."

"And it was the duty of young Muslim men to stand up

"and to defend the Muslim nation. And to fight back, if necessary."

Months after leaving Britain,

the boy from the backstreets of Birmingham

is on a journey towards the upper echelons of Al-Qaeda.

When Rashid Rauf went to Pakistan,

he married into a family of Kashmiri royalty, if you will...

..and he generated all these connections.

He became an important cog in that terrorist community.

Rauf fully subscribed to the Al-Qaeda narrative...

..and because he was resourceful, articulate, and clever,

he quickly rose up their ranks.

It's a trajectory, this extraordinary journey.

He is now, in those early years,

seen as something of Al-Qaeda's point man.

Working in the wilderness of north-western Pakistan,

it is believed Rauf is promoted into a key position,

an organiser and a talent spotter for the terror network.

What these training camps represented

was not just training in the use of arms and explosives,

but also giving these young men

a tremendous sense of solidarity and community.

His role would later put him on watch lists worldwide.

Absolutely a key character, and very much a focus

of international concern.

We were worried about him. The Pakistanis, of course.

The Americans were very much focused on him.

He was the person who turned ambition into reality.

He was absolutely working at the senior levels of Al-Qaeda,

and he was the bridge to external operations.

He was vetting a large number of young men going into these regions.

He was able to suss out and decide very quickly

those who were up to the job and those who weren't.

AKI PERITZ: He had the ability

to nudge people along the path of violence.

Here, at the height of the war on terror,

it is thought that he has become

one of the world's most dangerous terrorists,

who turns believers into bombers.

And among them, the architects of Britain's most devastating attack.

SIRENS

NEWSREEL: Appalling scene.

The top of this double-decker bus blown clean off.

On 7/7, four suicide bombs explode on London Tubes and buses.

52 people lose their lives. Over 700 are injured.

7/7 was a horrific attack.

A reminder of the willingness of terrorists

to try and target the vulnerabilities

of an advanced society and an advanced economy.

Should we have been able to stop this?

Is there a failure here on our part?

It's a very emotional thing. It's a point of very great stress.

And, just two weeks later, terrorists strike again.

On 21 July, there was a second wave of attacks.

This is not a one-off, and that's the end of it.

This is part of a pattern.

This time, the bombs fail to fully detonate.

NEWSREEL: Out of the darkness emerged two men.

The would-be attackers are arrested.

According to reports,

Western intelligence officials identified Rashid Rauf

as a figure connected to both waves of attacks in London that summer.

He was later acknowledged

as the author of a review for Al-Qaeda,

a kind of internal audit of why the 21/7 attack failed.

Rauf realised that he needed to stay in constant contact

with the conspirators

because sometimes people don't follow directions.

These are young men who maybe aren't the best students,

and so he knew that he had to talk to them.

Al-Qaeda saw him as a valuable commodity.

He had the zeal, and he had the leadership

to make these people carry out attacks.

During that time, from, I'd say, 2002

until I left the police in 2008,

it was ceaseless, absolutely relentless.

One plot after the other.

According to US intelligence,

Rauf is already working on the next attack.

He's building a new cell in Britain.

At the heart of it, 25-year-old Abdulla Ahmed Ali.

Abdulla Ahmed Ali was British-born, lived in Walthamstow.

He went to high school, went to university.

He seemed like a very normal person.

Very capable, very sharp, clever.

And people describe him as being charismatic.

Usama Hasan, from East London, once travelled abroad for jihad

and now advises on counter-extremism and deradicalisation.

For someone like Ali, and for, actually, tens of thousands

of young men of British-Pakistani origin

who were very aware of their identity as Muslim,

they certainly had a sense of a politicised identity

and were aware of the racism growing up,

which was increasingly replaced by Islamophobia.

In 2004, shortly after losing his first-born child to ill health,

Ali makes extended trips to Pakistan.

Empathy for the plight of his fellow Muslims

evolves into anger and extremism.

This is a man who was fired

by a great sense of both personal injustice,

but also a man with a great sense

of his community having been gravely harmed by Western power.

This hardened his heart against the Americans, against the British.

He wanted to join the jihad in Pakistan,

and then that's when he basically met Rashid Rauf.

In Ali, it is said, Rauf spots potential.

Ali was a smart guy.

What was also important was that he was considered a leader.

He could motivate other people.

If you compare him to someone like Rashid Rauf,

the reports that I have read is of a man

who was much fiercer in his manner and his conduct.

Al-Qaeda realised that these British-born individuals

who want to commit to the jihad, if they were sent to Afghanistan,

they'd be chewed up within a month and they'd be dead.

It was better to send them back to the UK

and use them as cells for a future attack.

Ali returns to Britain to build a terrorist cell.

What he doesn't know

is that British security services are already onto him.

He had come onto our radar originally

two or three years earlier because he was involved

in facilitating people to go to Pakistan.

But at that stage, we didn't think that he was an actual plotter.

That started to change when we realised that he was in touch

with the people in Rashid Rauf's circle in northern Pakistan.

Ali spends months establishing a cell in Britain

with one clear purpose -

to pull off a terrorist attack that could kill more people than 9/11.

ROHIT KACHROO: British security services are monitoring

a suspected terror cell operating in the UK.

It's being overseen from Pakistan by Rashid Rauf,

a 25-year-old from Birmingham.

They also know that its leader is Abdulla Ahmed Ali,

who has just flown back to London.

But what's not clear is why.

CHRIS: Ali had gone to Pakistan. He returned.

He came back through the airport.

He was on our target list, and we were looking at him.

We examined his luggage,

and in his luggage, there were batteries.

Quite a number of batteries, which had been purchased in Pakistan,

which is a strange thing to do.

Batteries had been used as detonators.

We had seen that before.

So that was an indicator that said, "This is something serious."

And it moved it up the scale of operations.

Maybe he was actually involved in direct plotting

to mount an attack here.

He became the focus of our surveillance.

That was really the beginning of the investigation.

By late June,

a massive counter-terrorism operation is under way.

It's codenamed Operation Overt.

Led by MI5 and Scotland Yard,

it would become Britain's biggest-ever surveillance operation.

Certainly, the coverage of Ali became more intense after that.

We needed to find out much more about him -

what he was doing, who he was meeting,

and ideally, what were his intentions.

Anna is an MI5 officer.

This is the first time a serving spy

has spoken publicly about working on Operation Overt.

She helped to track Ali's movements,

and she describes how his trip from Pakistan

set in motion an unrelenting six weeks.

ANNA DISTORTED: You cease to have any kind of life

because you're just living in the office.

What should have been very long days flashed by in a blizzard

of just trying to keep on top of everything.

I think we were using pretty much

all of the surveillance teams across the UK,

in terms of MI5 and police resources.

It was really, really busy. Nerve-racking.

The alarm bell is heard across the Atlantic,

as warnings about the threat

are shared between London and Washington.

What I remember vividly is how intense the level of secrecy was.

The amount of intelligence gathering,

the amount of coordination and cooperation

is rather extraordinary because from Washington,

we were getting a very clear view of what was transpiring.

By mid-July, all eyes are on Ali.

Ali is being tailed at this point by surveillance officers.

He goes to Lloyd Park in Walthamstow,

and he meets an individual who the police had no idea who he was.

But this is where Assad Sarwar enters the picture.

CHRIS: We did not know who that individual was.

They do something very strange,

which is that they lay down in the middle of the park,

and they put their hands over their mouth, like this.

That was a clear indication of tradecraft.

They were guarding what it was they were saying because they feared

they may be being filmed or lip-read, etc.

That told us that these were professionals.

This was a cell that had training.

And if you think about that as an operational challenge

for an intelligence service,

that is very difficult because you can't hear it,

you can't see it, you can't really approach it.

Assad Sarwar becomes an important focus.

It looks like he's been living a quiet life

at his parents' house in High Wycombe,

but it soon becomes clear that he'd been busy for months.

We had coverage of Sarwar.

He was going around the country using false names

and bulk-buying hydrogen peroxide.

Hydrogen peroxide is something you can buy

in every drug store in the world.

You use it to clean cuts, use it to dye your hair.

But if you boil it down to a certain percentage,

it can become extremely unstable and explosive.

There were elements that we recognised from the 2005 attacks,

so the use, for example, of hydrogen peroxide.

And once we started to see them acquiring those items,

all of that sort of fits the pattern.

Email messages from the time show Sarwar is under pressure

from superiors in Pakistan overseeing the cell.

The emails indicate the progress he's making

acquiring the bomb materials.

The stockpile soon grows

way beyond what Sarwar can store at his parents' house,

so he needs a new plan.

In late July, he heads to King's Wood in High Wycombe,

but he's being trailed by Thames Valley Police.

Sarwar going into the woods at night

creates a massive difficulty for a surveillance officer.

You cannot follow someone into woods

because, clearly, you don't expect to see anyone else

at that time of day.

So, for the surveillance team, it really is a nightmare.

Sarwar makes repeated visits over many nights,

but officers can't be sure what he's up to.

We realised that what he was doing was he was gonna hide the suitcase.

He would go late at night into the woods, dig a hole,

hide his stuff and then retreat

before anybody realised he was there.

I think it was quite clear that he was struggling

with the role he'd been given.

It was probably beyond his capabilities.

And one of the reasons around that is he had googled how to dig a hole.

What Sarwar did manage to stash away was significant.

Police would later discover over 40 litres of hydrogen peroxide

hidden in woodland near his parents' house and in their garage.

It took a long time to find it.

It was hugely significant -

precursor chemicals for making bombs

and other bomb-making material.

Sarwar isn't the only person of interest connected to Ali.

Police tracking Ali's movements over the summer

would identify 24 suspects in the group.

As we continued surveillance,

we started to see a network getting together.

The number of targets started to increase,

that were not only seen as associates,

but they were active associates.

To investigators, the warning signs are gathering.

Weeks before Sarwar's surveillance in the woods,

a relative of Ali purchased a flat in Walthamstow, East London,

for £138,000 in cash.

By late July,

some of the suspects are seen going in and out of the property.

It was quite clear that we needed to know what was going on in there.

And the only way to find out is to be in there with them.

A branch of MI5 are probably the best in the world at covert entry.

There is a risk of compromise, but at that level,

we discussed that the intelligence and information we would get

outweighed that risk.

But for MI5 officers on the ground,

the most precarious moment is still ahead.

ANNA: When the door opened and you're looking up into the darkness,

you're not quite sure if there's anyone in there.

ROHIT KACHROO: British security services think they've identified

a terrorist hideout in East London.

Men linked to what would later be known as the liquid bomb plot

have been seen going in and out.

DAN: There was an imperative to get in there

and find out what these guys were doing.

Dan is another MI5 spy,

speaking for the first time about Operation Overt.

I've worked on hundreds of operations.

Lots of entries - terrorist properties, mainly.

Sometimes you're breaking into someone's house,

you're standing in a terrorist's living room, and they have no idea.

Dan and his colleague, an MI5 locksmith,

wait until they believe the property is fully empty.

And then we move forward.

It feels like the clock's ticking.

We're through that door very quickly.

If you've been in MI5 long enough, you're going to be involved

in investigations or operations where people have been killed.

When the door opened and you're looking up into the darkness,

and you're not quite sure if there's anyone in there,

and you think, "God, if I fuck this up,

"this is gonna bring to an end

"maybe the biggest counter-terrorism investigation

"in the country's history."

There's a degree of pressure,

and, obviously, there's a potential consequence

of not just fucking up an operation, but being hurt.

You're using almost no lights.

You're not giving the game away.

If you open a door, if it's ajar, you make sure when you come out

you put it exactly to the same position it was in before.

The flat is littered with suspicious-looking items.

There was a row of bottles lined up, sort of neatly equidistant.

They all seemed to be empty.

That all seemed very odd.

This box contained different glass jars.

There was one that was full of batteries.

There was a big jar full of some white, gloopy liquid.

There was a bit of banter back and forth about, you know,

"Cut the blue wire" and "Don't drop it".

At the end, we put the things back,

and I said to the locksmith, "Sometimes I fucking love my job."

Over the course of five nights,

Dan's team install hidden surveillance equipment.

We want as much audio and CCTV coverage as we can

of the key parts of this flat.

So that's audio in every room,

and, clearly, CCTV in the kitchen is gonna be key.

What surveillance later sees inside the flat is confirmation.

The preparations for the plot are real and in progress.

The fact that we could actually watch live as they were doing this

was absolutely vital, of course,

because it confirmed to us that they were building devices, bombs.

And the way that they had designed

was to create a liquid explosive, effectively,

to hide that in a drinks bottle

by drilling through the bottom of the bottle,

inserting the explosive and then sealing it again with resin.

The plotters replace the original drink with hydrogen peroxide,

and they used a powdered mixture called Tang

to mimic how the drink used to look.

And then you've gotta work out, how do you make the bomb detonate?

And they did that by taking disposable cameras,

and then they had adapted the battery and so on in that

to be a detonator.

You've got your drink bottle, you've got your camera,

you can then wire those together,

and, in fact, you have created an effective bomb.

The bomb components discovered in the flat

are not yet viable or fully assembled,

but the intentions are clear.

Hidden microphones pick up more.

CHRIS: We picked up conversations talking about a list of names.

So, they went through a list of about 18 individuals,

and some of them were nicknames, and some were names of the team.

18 members of the cell are identified,

meaning there could be as many as 18 attacks.

What really struck me was the speed with which

the key members of the core of this plot

were able to recruit and persuade young men...

..and they were all young men...

..that they should kill not only themselves,

but also thousands of members of the public.

One of the alarming things that I heard in the flat

was Ali discussing taking his wife

and his young child on the flight with him.

That indicated just how serious these individuals were,

that they would take their child and their wife.

That's quite alarming.

Intelligence on the bomb factory is shared Stateside.

The CIA digs deeper.

WAYNE MCCOOL: There was one particular meeting

that I attended down at the White House.

And the discussions at the time was about the efficacy of the device,

and whether or not it would function as designed

as the plotters were going to use it.

Because the question was, is this a real concoction?

And what damage could this do if it got onto a transatlantic flight?

We had to go forward and do some testing.

They worked as designed.

They went boom.

REPORTER: The device blew a hole in the skin of the aircraft.

At altitude, this would lead to the plane disintegrating.

JONATHAN EVANS: Within the UK, for evidential reasons,

we had to be able to prove that this was a viable device.

And the experts in the defence world built a replica of the device

and exploded it in one of their explosion chambers.

This was a real threat.

In London, as the city basks in the late July sun,

evidence keeps emerging from the Walthamstow bomb factory.

Some of my colleagues came in and said,

"You might want to come and listen to this."

ALI: Enough is enough.

We have warned you so many times to get out of our land, leave us alone,

but you have persisted in trying to humiliate us, kill us...

They were making suicide videos,

the videos that they would be issuing after the attacks.

INAUDIBLE

CHRIS: This gave us an indication

that they were coming to the operational phase.

So we knew that this was their last living will and testament.

They were clearly going to go through with this.

ANNA: I listened in live.

It was a really disturbing experience,

because these were pretty young men,

sadly, casually discussing not only their own death,

but the death of a lot of other people,

and trying to justify that.

This is revenge for the actions of the USA in the Muslim lands

and their accomplices, such as the British.

Six martyrdom videos would later be recovered by police.

The black banner and the anger and blaming world events,

and using it as a justification to kill

potentially thousands of innocent members of the public.

The plot is moving ever closer towards action.

In the government, the Home Secretary faces another choice,

with huge political risk.

The threat level to aviation is raised to critical,

but he's asked to keep that a secret,

to not tell the public.

JOHN REID: Severe meant an attack was likely.

Critical meant it was imminent.

I was getting pretty strong advice.

"You have to do this."

JONATHAN EVANS: And I said, "You can't do that.

"Because if you do that,

"the bad guys will realise that we're onto them,

"and then we might lose our access."

If, as a result of delaying, we miscalculated,

and the conspirators murdered 2,000, 3,000 people,

my judgment was that no government could have sustained that.

The government would've been in grave danger of falling.

And he said, "We're not going to publish the fact

"that the threat level's gone up."

Then he looked at me, and it's one of those points you remember,

and he said, erm...

"If this goes wrong, I'm out of a job,

"you're out of a job, and the government will fall."

Security services up the ante.

More than 800 police officers from across the country

are now monitoring 24 suspects around the clock.

People were brought in from Northern Ireland.

This was the biggest counter-terrorist operation

ever carried out, before or since, in the United Kingdom.

For the plotters, the preparations continue.

Ali went into an internet cafe in Walthamstow,

and the surveillance officers, brilliantly,

managed to get in there and see what he was doing.

CHRIS: Surveillance is a skill. It is an art, no doubt about it.

Ali was looking at flights.

He was looking up flight times,

flight locations from the UK to America

and was taking down the details of those flights.

And that was probably the first confirmation

that it was likely to be aircraft attacks.

Seven flights, all leaving Heathrow around the same time,

all bound for North America,

all potentially going down in the Atlantic.

The more you thought through the nature of this plot,

which was to bring down airliners,

sitting like ducks in a row over the Atlantic...

They wanted to do it that way

because then you would not have the proof of how it had been done.

The wreckage would've been somewhere deep beneath the Atlantic.

So it would've taken weeks, months, years, really,

to work out what on earth had happened.

Emails later that day from Ali to a contact in Pakistan

indicate that plans are only days away from being finalised.

That night, Abdulla Ahmed Ali and Assad Sarwar meet

on a street in East London.

But there's someone else with them...

..caught on police surveillance.

At first, officers can't work out who he is.

But it's Mohammed Gulzar, the old friend of Rashid Rauf.

CHRIS: Mohammed Gulzar appeared.

Which, at a time when you are undertaking attack planning...

..indicates that he is more than just a casual acquaintance.

It was quite clear that he had a degree of supervision.

In Washington, those revelations from the cafe in Walthamstow

are raising concerns.

I remember very clearly the President pressuring all of us.

He asked the question, "Are they on the brink?

"When can we take it down? Let's not wait too long."

It's almost five years since September 11, and its shadow looms.

9/11 was a national trauma of the deepest dimensions,

and part of that had to do with the perception of vulnerability.

I remember President Bush said to me,

within a day or two afterwards, "Don't let this happen again."

But this was a British-led investigation.

There was tension between the UK and the US on this.

We needed the time.

They needed assurance that this was gonna be closed down.

JOHN REID: Our judicial system is different from the Americans'.

If we take people in, we have to convict them on the evidence.

And if we go in with insufficient evidence,

then the very people we think are trying to carry out

the terrorist attacks will be back on the street.

It was very stressful.

You're weighing what is likely to be more dangerous...

..moving too quickly or moving too slowly.

As concern grows, more people in the UK government need to be told.

DOUGLAS ALEXANDER: I was on holiday with my young family

on the Isle of Mull in the Scottish Hebrides,

and I took a phone call

from the senior official in the Department for Transport.

He explained that he was sending a security official to brief me

on an issue that he wasn't able to discuss on an open line.

He came to the cottage where we were staying,

locked my wife and children in the conservatory,

in order not to breach, inadvertently,

the Official Secrets Act,

and then described to me, in some detail,

the plot that was anticipated.

The next morning, an RAF Lynx helicopter landed

in a field next to the cottage.

We took off from the Isle of Mull,

and we headed down the Pennines on the way to Battersea Helipad.

As I caught that flight south,

I felt a sense of responsibility, a sense of anticipation,

but I knew I was also heading into the unknown.

I'd been pretty busy for weeks. I hadn't had an hour off.

My office knew that I was a lifelong Glasgow Celtic supporter.

So they had booked me tickets

because Celtic were playing Chelsea in London.

So I went to the game.

And just after Celtic scored, I got a message saying,

"You may have to come back to the Home Office."

And then another one that alerted me

it was likely I would be asked to go back.

And then, just as Chelsea equalised, tragically,

I got one saying, "Get out now."

If I thought the game was exciting,

the travel back to the Home Office was out of this world.

I mean, there was a cavalcade of cars,

outriders, sirens screaming.

I never want to travel through London at that speed again.

The reason for the rush would soon become clear.

Events are unfolding in Pakistan.

The alleged mastermind of the plot is on the move.

ROHIT KACHROO: The plot to blow up

seven transatlantic airliners leaving London is ramping up.

But, unknown to the British security services,

their counterparts in Pakistan have sent the CIA

an important piece of intelligence -

that a key figure, the alleged mastermind of the plot,

Rashid Rauf, is on the move.

AKI PERITZ: Rauf was moving from one part of Pakistan to another.

He'd left one of his cellphones on, which pinged on a tower,

which meant that they knew exactly where he was,

and they saw that this ping was moving.

It's a rookie move.

And it just turns out that Rauf made a mistake.

Rauf is on a bus that comes to a stop

near a checkpoint in rural Pakistan.

Police on the ground sound the alarm.

And the call says, "We have Rashid Rauf. He's in a bus.

"He's coming up to a checkpoint. What should we do?"

The CIA and Pakistani security services

give the nod to arrest him.

Take him out.

We have to take this senior terrorist out

when we get the chance, because he might disappear.

He was so comfortable that he was asleep when the bus stopped.

Taking him out of the battlefield was a huge success.

Those type of... perishable opportunities

do not come along very often.

It could have been a couple of years

before they would have another opportunity to do that.

I remember a sense of relief.

I knew that there was probably consternation

on the part of our British colleagues

because of how aggressively this had been undertaken,

and when it was taken.

Back in London, British officials feel blindsided.

The Americans kept saying,

"We will not move without telling Britain first,

"so you can get all your ducks in a row

"to take down this plot all at the same time."

And then, suddenly, America unilaterally just moves in Pakistan.

Er, I think I issued an expletive.

It was more or less an expletive of, "What do we do now?"

It's fair to say I was disappointed.

Nobody on our side of the Atlantic wanted that to happen.

I understood the anger, but I also understood the American position.

They had lost 3,000 in 9/11.

They had explained that was because of a lack of intelligence.

This time, they had the intelligence.

There's no time to lose.

The worry is that after this unexpected twist,

the terror cell could be triggered into early action.

Hundreds of officers are mobilised

across the country and in Scotland Yard.

We set up an operations room,

supported by all the bells and whistles

that we could pull into play.

Time was against us at that point.

It was literally, go and find these individuals and arrest them.

It's just after 9:30 on the 9th of August.

In East London, surveillance police are tracking both Ali and Sarwar,

who are meeting up near Waltham Forest Town Hall.

I walked down to the operations room.

And at the time, Sarwar and Ali were meeting in a car park.

I saw them on the screen in the operations room...

..and I gave the order to arrest them.

We asked the surveillance teams to do things they never do,

which was to step in and arrest.

AKI PERITZ: The original officers did not have firearms.

And you had really no idea whether Ali was gonna fight back,

Sarwar was gonna fight back.

Were they gonna detonate a bomb that they did not see in the car?

And I said, "Walk up. Hands on."

There was no emotion from them.

They didn't try and struggle.

There was no reaction.

In Ali's pocket was an address book...

..which had connectivity to some of the operational emails.

In the book, what looks like simple checklists, even games,

that the police would later decipher as code for contacts in Pakistan.

And a memory stick found on Ali would be recovered,

containing a list of flight timetables.

Throughout the night,

suspects are plucked off one by one -

on the street, in cars, at home.

I can confirm that a significant number of people

are currently in custody, and the operation is ongoing.

The operations room included a whiteboard

with very simple pictures of all the suspects who needed to be arrested,

with their names and their codenames underneath.

And as each one was safely detained and brought in,

someone would shimmy across and place a little red magnetic dot

on their face to show they were safely detained.

And at the very end, there was a sea of red dots,

and there was one face left.

And as we're all stood there, at the last moment,

one guy sort of sidles in underneath

and places this last red dot on this face,

and a big cheer went up in the operations room at that point,

that we knew at last, our immediate duty, at least,

to the safety of the public, had been discharged

because all of the suspects had been safely detained.

One of the suspects arrested refuses to open the door to police,

forcing officers to break in and detain him on the floor.

He gives police a false name,

but his fingerprints later identify him

as Mohammed Gulzar,

friend of plot facilitator Rashid Rauf,

who left with him to Pakistan in 2002.

In total, 24 suspects are arrested.

In all my over 30 years of policing,

that was the most satisfying and important night

of my entire police service.

As suspects are taken into custody,

COBRA, the Government's emergency committee, urgently convenes.

The threat is far from over.

There was intelligence that they were thinking

not just of one wave of attacks, but maybe a second wave.

We can't be absolutely sure that there weren't other people

who were part of the plot who we hadn't come across.

Even though the plot is foiled, there will be consequences.

And Britain's airports are where they're felt first.

I was in constant contact

both with officials but also with the airlines

and indeed with Heathrow Airport

and other airports across the United Kingdom.

We had to stop incoming flights.

We had to stop outgoing flights.

And we had to change the security regime,

all in the course of a single overnight.

This is the moment the world finds out

about the transatlantic bomb plot.

Overnight, the police,

with the full knowledge of ministers,

have carried out a major counter-terrorism operation.

Ensuring maximum security, unfortunately,

will involve immediate and severe disruption for passengers,

with significant delays likely at all UK airports.

Security measures, longstanding routines at airports,

are overhauled overnight.

All hand baggage will now have to be checked in,

with only a small number of essential items

allowed through search controls.

Liquids are banned on board,

with a 100ml limit enforced in the months to come.

Exceptions will be in place for those travelling with infants

and for prescription medicines.

We didn't have the scanning technology

to be able to tell whether the liquid was benign

or whether it posed a genuine threat to the viability of the aircraft.

As the sun rises,

airports in Britain are quickly overwhelmed.

Security services clearly believe

there may still be bombers on the loose,

as unprecedented checks have been put in place

at airports like this one,

with almost no hand luggage being allowed on planes.

LISA MINOT: There was total chaos.

It's the height of the school summer holidays.

The airports are packed, thousands of flights cancelled.

You've got passengers stranded in terminals.

I's just really annoying, not knowing what's going on.

Heathrow was the hardest hit,

with more than 600 flights cancelled by mid-afternoon.

There were queues out the doors, into car parks,

big police presence,

police dogs patrolling the crowds,

a real sense of fear inside the terminal.

People didn't know what was happening.

Any liquids discovered must be removed from the passenger.

We will not be permitting bottled liquids and fluids.

There were huge piles of high-end toiletries,

perfumes, alcohol in vast bins,

stacked up on crates,

taken off of people as they tried to go through security.

Mothers were being told that if they wanted

to take their baby's milk on board,

they had to taste it in front of a security guard

to make sure that it was actually milk.

This was a seismic shift in the way that we travel.

As the world tries to make sense of a new way of travel,

six weeks of Operation Overt have come to a head.

For Anna and her MI5 colleagues,

the sacrifices have been significant.

I dropped off the face of the earth for a few weeks...

..not long before I was due to get married.

And that's the point that my fiance and I decided

that we probably needed to tell our parents

what I did for a living,

so that they didn't think I'd gone flakey.

But, I mean, these are the kind of jobs that we all join to work on.

In the following days and weeks,

British police gather an enormous haul of evidence.

PETER CLARKE: The scale was bigger

than probably anything else we'd done.

But the plotters had not yet bought flight tickets,

and the bombs were not yet viable.

There are multiple trials.

REPORTER: All eight men accused of plotting to blow up aircraft

deny the charges, and the case continues.

And in the second trial, in 2009,

Ali, Sarwar and Ali's friend Tanvir Hussain

are convicted of a plot to bomb transatlantic flights.

Five others are found guilty of conspiracy to murder.

And two more are convicted of terrorism preparation offences.

But what, then, of Mohammed Gulzar,

the man who met Ali and Sarwar

just three days before their arrests?

He is acquitted.

He did not record a martyrdom video, nor did he enter the bomb factory,

and there is no conclusive evidence against him.

But investigators believe emails discovered later

might have changed that outcome.

Those emails showed Gulzar had lied in court.

And at Ali and Sarwar's retrial,

they both accepted that Gulzar had been sent to them

as an explosives expert.

CHRIS: There was information in those emails

that showed Gulzar's role.

I then submitted a report to the CPS

saying that we now have new evidence,

and we were looking for a retrial.

The reply that came back was that they didn't feel

it reached the threshold.

I think the fact we didn't have that intelligence,

and we didn't understand his role, meant we couldn't prove it in court.

Today, Mohammed Yasar Gulzar still lives in the West Midlands.

He declined our offer to contribute to this programme.

As for Rashid Rauf, the boy from Birmingham,

he suffers a different fate

following his arrest in Pakistan in August 2006.

At one point, he makes a court appearance,

and then, several hours later, he disappears.

He never shows back up in his prison cell.

So, what happened to him?

And the answer is, we don't really know.

MICHAEL CHERTOFF: I was unhappy, to say the least,

that he had escaped.

And, of course, we were always concerned about how that happened.

Was that aided and abetted by some insider?

When we heard that,

we, I have to say, raised our eyebrows.

I don't think we ever got to the bottom of it.

After he escaped and went back

to the Federally Administered Tribal Areas of Pakistan,

he spent some time doing external operations.

American intelligence officials believe that Rauf was killed

in a US drone strike in November 2008.

He died in an explosion with other Al-Qaeda members

outside of Mirali in North Waziristan.

Twenty years on from the arrest of the plotters,

the world would look so different today

had the attackers been successful.

We would not have recovered fully from this.

You would've had, probably, a death toll higher than 9/11.

There would have been a terror

in people's hearts.

Our psyche was already heightened. We were already scared and worried.

Honestly, I think you might not even have civil aviation now.

People would not have flown.

Partnerships would, perhaps, be broken.

The fact is that the United Kingdom would have been used

as a launch pad to attack America.

But instead, a terror attack was intercepted.

We got everybody. Nobody lost their lives.

The guilty were convicted.

Groups like Al-Qaeda

were forced to switch from organised spectaculars

to lone-wolf tactics.

Stabbings and car rammings became the trademark

of modern-day terrorism.

And ultimately, whilst our way of travel might have changed,

there is so much more that was protected.

DOUGLAS ALEXANDER: Thank God for what was achieved that night.

Thank God we were able to avoid

the level of chaos, destruction and fear

that would've unfolded rapidly

if we'd seen those airliners brought down.

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