A busy mall in a major British city: beside the benches in the main concourse, where shoppers sit checking their phones, a unremarkable-looking young man, casually dressed, takes off his rucksack, places it on the floor, crouches down and starts rummaging inside.
If anyone was watching closely, they would notice his fingers shaking as he undoes the zip.
Now his eyes are closed and he is momentarily still, as if lost in thought or prayer. Suddenly, he springs to his feet, an automatic weapon in his hand, ready to fire indiscriminately.
This nightmare is, I must stress, a fiction, the final scene of The Attack: Terror in the UK, to be broadcast on BBC 2 tonight, but the drama is based on real-life attacks by terrorists caught up in the favoured tactic of Islamic State of Iraq and the Levant (Isil) of seeking ways to carry out mass killings in the shortest amount of time.
And, as Max Hill, the newly-appointed independent reviewer of terrorist legislation, warned in this paper at the weekend, Britain is right now facing an “enormous on-going risk” of “indiscriminate attacks on innocent civilians” that in his opinion is unparalleled since the IRA attacks of the 1970s.
“This is the style of attack that is most feared by the professionals,” confirms Richard Walton, a consultant on the BBC drama who, for five years until 2016, was Commander of SO15, Scotland Yard’s counter-terrorism unit.
His face – open and surprisingly unlined for someone who spent almost all of a 30-year career in the police trying to keep one step ahead of terrorists (though he was also involved in the Stephen Lawrence case) – tops and tails The Attack, delivering a commentary that grounds in reality the shocking events it depicts.
“MFTAs” as they are known in his world of surveillance – Marauding Firearms Terrorist Attacks – have, he admits, been keeping him awake at night since November 2008 when, in the Indian city of Mumbai, a Pakistani Islamist terrorist organisation linked to al-Qaeda first adopted the tactic to carry out a series of shooting and bombing attacks at locations that included the landmark Taj Mahal Palace Hotel, killing 164 and wounding over 300.
“That was the time everyone in my world woke up to the fact that, if terrorists started using arms in this way, they could probably kill a lot of people in a short period of time. And this attack methodology is the one promoted by Isil.”
The horror of Mumbai has subsequently been repeated – most recently in Paris, as well as in 2013 at the upmarket Westgate Mall in the Kenyan capital, Nairobi. Commander Walton was involved in the aftermath of that attack.
So should we all be lying awake at night too? Last August, spy chief Alex Younger, head of Mi6, warned publicly that Isil “is plotting ways to project violence against the UK”.
He referred to 12 such plots that had been foiled by police and intelligence agencies since June 2103. Younger’s words made it sound as if it was only a matter of time before the sort of carnage imagined in The Attack happens on our streets.
“We have to be constantly foiling them,” says Walton. “If you take the last three years in France, there have been 18 terrorist attacks, with over 130 people killed. In Germany there have been five.
In Belgium five and in the UK not a single one.”
And that, he adds, isn’t down to luck. “There isn’t much luck. You can minimise the need for luck by being very sophisticated.
The key to do it is to join the work of the intelligence agencies with the police, in a smooth day-to-day operation so that information doesn’t fall into the cracks. That is when you get killings.
We’ve worked very hard on that in the UK but I think other countries in Europe are still struggling with that concept.”
Nipping plots in the bud is vital, he explains, because, however well prepared the police are, they cannot immediately stop a terrorist brandishing an automatic weapon in a shopping mall before he or she fires it. “Once they start, regrettably, people will die, regardless of how fast the police response is.”
The challenge, he explains, is constantly evolving, so there can be no grounds for complacency. The likely collapse of the besieged Isil “caliphate” in Mosul, for example, may trigger a return of some of the 850 UK citizens who have embraced radical Islam and gone there to fight.
Walton, though, refuses to be daunted. The resources are in place, he says, for the 600 or so active terrorist investigations currently being carried out by police and the intelligence services. “Some fighters will return, but many have already come back and we’ve met that challenge. I’m optimistic the threat will diminish with time.”
Another cause for concern – highlighted in The Attack – is the radicalisation of other prisoners by the estimated 178 Islamist terrorists who are already behind bars. In the main storyline, Joseph, a vulnerable young man connected with organised crime and therefore with ready access on the outside to guns, is first befriended and then radicalised in jail by a group of Isil sympathisers.
“There isn’t much overlap outside prison between terrorism and serious and organised criminality,” reflects Walton, who remains involved in the counter-terrorism world as a private consultant. “But where it does come together is in prison. It is very hard to have strategies to combat this given the wrong circumstances.”
He points to Michael Adebolajo and Michael Adebowale, who murdered Drummer Lee Rigby outside his barracks in Woolwich in May 2013. “Both had had recent times in custody and came under some influence there that we thought was a driver to the attacks.”
Regarding radicalisation in the wider community, however, he is more reassuring. The government’s Prevent strategy, designed to counter this threat, works effectively, he reports from first-hand experience. “Prevent gets a bad press but I can tell you it has prevented terrorism.
Most Muslims in Britain know what it is about and they support it. The numbers are now up to 700 referrals every month nationally, many from individuals. That is a lot of people ringing in.”
So why the criticism of Prevent? “You need to look at who is making it. It is often being criticised by those who are apologists for terrorism, who for their own political ends say it’s ‘spying’ on the population.”
Strong words, but a reflection of just how high this front-liner in the fight against terrorism believes the stakes to be for all of us. “When I started as head of counter-terrorism in 2011, the numbers of operations we were engaged in were much smaller. Prior to the advent of Isil in 2012-13, it was a relatively small number of British Muslims who were going to join al-Qaeda and, therefore, much easier to monitor them.”
What changed was the creation of the so-called caliphate in Iraq and Syria. “The way in which it was done was a masterclass in marketing. It managed to entice as many as 30,000 Muslims to go there to join, from between 85 and 100 countries around the world, according to some estimates.
The brainwashing is very powerful and so terrorism has gone from a niche activity to a volume business. We are dealing with high numbers of extremists.”
In such circumstances he cannot, he says, offer any copper-bottomed guarantee that the sort of incident imagined in The Attack won’t ever happen in our cities.
“You can’t ever be totally 100 per cent confident you can stop terrorist incidents happening. You are making judgments all the time and you know if you get them wrong, the consequences are devastating.”