At a primary school in west London, a class of 10-year-olds are acting out the story of the gunpowder plot. A small boy playing the hardline Catholic Robert Catesby persuades another to join his plan to blow up Parliament.

Guy Fawkes creeps about in front of the blackboard, pretending to plant explosives in the cellars of Westminster, until he is caught red-handed.

Tamara, a cheerful drama student who is running this class on extremism, halts the charade to explain that Fawkes was as much victim as criminal. “He was only the plotter’s friend,” she tells Year Six. “It wasn’t his fault that he was radicalised.”

This training session, delivered by the charity Just Enough, is part of Prevent, the UK government’s ground war against violent extremism. The programme is the most controversial aspect of its counter-terrorism strategy, seeking both to educate communities on the risks of radicalisation and to stage interventions with vulnerable individuals long before any crime has been committed.

The double-decker bus blown up in Tavistock Square, central London, during the July bombings in 2005 © Peter Macdiarmid/Getty Images

Founded quietly in 2003, then expanded after the 7/7 London bombings, which killed 52 people, Prevent started on a small scale. But a rising drumbeat of terror attacks over the next decade prompted calls for expansion.

After the murder of fusilier Lee Rigby outside an army barracks in south-east London in 2013, prime minister David Cameron told parliament: “When young men born and bred in this country are radicalised and turned into killers . . . we have to do more.”

What emerged was a tougher approach to pre-criminal extremism than in perhaps any other country. New legislation requires public officials working in schools, universities, hospitals and local councils to report on individuals showing radical tendencies.

The Home Office claims that, so far, the programme has successfully diverted more than 1,200 people from extremism and, potentially, acts of terror. After more than a decade operating in relative secrecy, the department is gradually lifting the veil on its methods, allowing the FT unprecedented access to a handful of Prevent staff working in London and Kent.

Nik Adams, a senior police officer working in counter-terrorism, describes Prevent as a process of “brilliant and professional people recognising how significant the seemingly insignificant might be”.

But critics of the programme — including human rights lawyers, some teachers and representatives from the Muslim community — argue that, on the contrary, this approach encourages well-meaning public officials to look for threat where it doesn’t exist. Such statewide surveillance, they warn, is not only discriminatory but actively counter-productive.

Even more damaging is the suggestion that Prevent’s deradicalisation programmes simply do not work. Last year, a private report by behavioural psychologists in Whitehall cast doubt on the effectiveness of the programme, questioning whether there is any evidence base behind its methods.

Opposition to Prevent has reached such a pitch that this week the Home Office suddenly announced an independent review, due to begin later this year. Addressing parliament, security minister Ben Wallace challenged Prevent’s detractors to provide “solid evidence” of their allegations, and move beyond what he called the “distortions and spin” used to discredit it.

Kent is a large, sprawling county on the heel of England known for its fruit farms and rolling hills, but the number of Prevent referrals here is high, and rising. Caught between London to the west and the English Channel to the east, its wealthy, green commuter belt belies patches of deprivation: coastal districts such as Thanet, where unemployment is high and educational attainment low. It is an uncomfortable locus for the twin strands of Prevent work — Islamic extremism and far-right radicalisation.

Nick Wilkinson, head of Prevent for Kent County Council, juggles these risks in a state of constant vigilance. A retired police officer, he was inspired by his father, who worked on Northern Irish terrorism for Special Branch.

His first taste of national security came at the age of three, when he asked his dad what he had done at work that day and was told: “I can’t tell you.” The 56-year-old started the Prevent job at a critical juncture in 2015, when the number of unaccompanied child migrants arriving at Kent’s ports reached a historic high of 948 in a year.

These youngsters from the Middle East present a complex security predicament: they land at Dover separated from their families, often traumatised by their journey. The council must find them foster families and education, and support them through the Home Office’s asylum application process.

“They will have incredible vulnerability around their mental state, around the trauma that they have experienced. One of the key strains is loneliness,” Wilkinson explains. “On that journey they would have developed different relationships, perhaps different stories, and so when they then land in the UK, how do we really know who they are and where they come from?”

When a bomb partially exploded on the London Tube at Parsons Green in 2017, the attacker was found to be Ahmed Hassan, an 18-year-old Iraqi who had arrived in the UK two years before as a child asylum seeker. He told immigration officials processing his asylum application that he had been groomed by Isis and “trained to kill”, so he was referred to his local Prevent team in Surrey, which neighbours Kent.

However, his case was mismanaged and the resulting attack sparked scathing criticism from parliament’s Intelligence and Security Committee, which said the failure to contain Hassan exposed “deep-rooted issues” in the management of Prevent.

That is the issue: we’re going for the people which are softer, not the hardened ones

Wilkinson is determined to avoid a similar disaster on his patch, but is also battling a growing threat from far-right extremists. Kent’s seaside towns are home to several poor, predominantly white communities that feel remote from the metropolitan diversity of London.

The county has become a centre for protests by far-right groups including the English Defence League, Combat 18 and White Lives Matter.

To limit the threat, Wilkinson has trained 18,000 local staff on the signs of radicalisation in the past two years. They come from all areas of council work: child safeguarding, adult social care, mental health services, schools, housing and healthcare, and are taught to spot worrying signs among pupils, patients or council tenants, from becoming suddenly uninterested in everyday activities to hiding a new lifestyle, religion or political allegiance from family and friends.

One grey, wintry morning, I join more than 50 Kent council employees in an over-heated lecture theatre. We are shocked to attention by a photograph of an 11-year-old British boy appearing to execute a kneeling prisoner in an orange jumpsuit.

Taken from Isis propaganda, this is the son of infamous “white widow” Sally Jones, a former punk rocker who left her home in Chatham, Kent, in 2013 to marry a jihadi in Syria. Wilkinson describes Jones as a “Kent mum, from a Kent village”, whose son went to a “Kent school”. Both are now thought to have been killed by a US air strike.

Khalid Masood, the terrorist who murdered five people in Westminster in 2017, grew up in Dartford, Kent, and was educated in Tunbridge Wells, Kent. Next, BBC headlines flash up on the screen, describing the arrests of two teenagers in Ramsgate, Kent, on suspicion of preparing terrorist acts inspired by far-right ideology.

Wilkinson tells us about a man who was referred to Prevent by a doctor who spotted Isis slogans on his T-shirt, and a teacher who called in after a pupil submitted racist posters to a school project. He has given this lecture hundreds of times, but there is still an urgency to his delivery. “Why would you not want to stop terrorism?” he asks. “The threat is local.”

After these training sessions, the phone calls and emails begin trickling in. Wilkinson and his two Prevent colleagues, Helene and Natalie, share an office on the first floor of the County Hall building. It is here that they gather and assess intelligence. “We do have a larger number of referrals in Kent than they do in some other places,” Wilkinson says.

His approach is about covering every possible contingency, being “watertight”, he tells me repeatedly. “It is a constant battle to ensure that frontline workers really understand what this is about. That can be from the UK Border Agency through to the social care workers, through to the voluntary sector, who are trying to support some incredibly vulnerable people.”

After the 2017 attack n Westminster © PA

The most sensitive part of Prevent is deciding whether a tip-off merits a formal referral: if it does, this triggers a triage process to determine what type of intervention is needed. Minor cases may be sent on to other council services such as parenting support for families whose children are watching inappropriate videos online.

Cases thought to present a real risk of violent extremism are escalated to the most intensive level of Prevent, known as Channel. At this stage, counter-terror police will be involved in the management of the case and will receive information from counsellors, social workers or theological mentors working with the individuals concerned.

Every Prevent team in the country is expected to host a monthly meeting of police, healthcare specialists and social workers known as a “Channel panel” to determine which individuals should be offered this level of intervention, and to monitor the existing caseload.

According to the Home Office, 7,318 people were referred to Prevent in the year to March 2018; of these, 1,314 were put forward for discussion by a Channel panel. However, only 394 — or 5 per cent of all referrals — went on to receive Channel support. Since engagement in the programme is strictly voluntary, it may be the case that more than 5 per cent were offered help but some turned it down.

Why would you not want to stop terrorism? The threat is local

Making sure the right people get on to Channel and stay on it is the most important call that Prevent staff make. Ahmed Hassan, the Parsons Green bomber, had been referred to the Channel process but Surrey County Council, which was managing him, did not convene a panel for six months, during which time Hassan’s mental health deteriorated.

His foster carers reported that he was going missing, but this was not considered noteworthy by the police who were reporting to Channel. Ten days before the attack, the panel met and discussed closing Hassan’s case.

Wilkinson is deeply critical of Surrey’s failures but he admits that even a well-run team will question its decisions. “Have we had the right number referred? I don’t know. I constantly push it back. If something kept me awake at night, it would be one of those [unaccompanied children] popping out to do something.” “To do what?” I ask. “A terrorist attack,” he replies.

In a chicken shop on London’s Elephant and Castle roundabout, Anjum Khan is eating a burger and discussing how to bond with extremists. Khan, a Sunni Muslim in his early fifties, has short grey hair, a goatee beard and an impish smile.

In the past decade, he has worked with more than 100 people, aged between eight and 60, referred to Channel. His job as a freelance mentor, contracted by the Home Office, is to challenge extremist views and address underlying problems such as feelings of anger, cultural displacement or resentment.

In his words, this means getting people “back to a factory setting of normal life”. Kebabs are his currency in winning trust: he meets his “clients” in chip shops and fried-chicken joints, then takes them for a dose of fresh air, pounding round parks while talking, questioning and offering another point of view.

He meets children at school during break time, or takes them out of lessons they are keen to avoid — usually maths, he says.

Ahmed Hassan, the ‘Parsons Green bomber’, who had been referred to the Channel programme © PA

Khan has a confessional manner but firm boundaries. He revels in his own anonymity, telling me “there’s a lot of Anjum Khans”. He reveals only that he was born in east Africa, moved to west London with his family aged five, and spent his twenties working in the entertainment industry. He hints at a wayward spell in Goa but had a “reality check” when his father was dying and he came home to take over the family’s corner shop. It was then that he reconnected with Islam.

His path to counter-radicalisation started with a job as a volunteer mentor, progressing to a career in youth offending and eventually running the first ever Prevent pilot in south London.

Now one of the Home Office’s most experienced “intervention providers”, Khan says his method is to persuade clients to take responsibility for their views or prejudices rather than blaming external factors such as “colonialist attitudes” or “foreign policy”.

A typical conversation with someone who has expressed hatred of the government or people of another religion might start by discussing their own circumstances. Do they live in a council property, supported by housing benefit? Do their children go to a state school? Isn’t their mother being cared for in hospital by non-Muslims? “So who is ‘them’?” he might ask his client. “ ‘They’ seem to be paying for everything.”

Many Muslim children . . . risk feeling they may be treated differently due to their faith

He also acts as a theological sounding board, questioning why the Koran is being used as justification for domestic violence or the formation of a caliphate. Khan uses his own religious knowledge — gleaned from a decade of reading the Koran while minding his shop — to push back against misinterpretations, and also consults Islamic scholars.

“Prevent works best in someone who has developed a vulnerability,” he says. “They don’t see it, but professionals have picked it up. We can address that vulnerability without them feeling that it’s compromised their religious beliefs.”

The Home Office asked me not to publish full details of Khan’s clients in case they could be identified, but his casebook is varied and colourful. He has worked with teenagers so disturbed that restaurants empty when fellow diners overhear their ramblings about death cults or fascism. He helped a boy whose father was showing him videos of beheadings. He spent weeks with an older white couple who converted to Islam and were determined to fight in Syria.

Some clients have tried to subvert the process, attempting to radicalise Khan. These are quickly referred upwards to police intervention. He caught out one teenager who appeared to have relinquished his extremist tendencies only to reveal himself in a WhatsApp profile photo glorifying jihad. He has so many stories of deradicalisation battles lost and won that it takes him two-and-a-half hours to finish the chicken burger he has ordered.

Khan is clear about where Prevent can do good, and has no time for public servants who criticise it, claiming they are only jealous of its funding at a time when government austerity has cut provision for other services such as youth groups.

He is scathing of fellow Muslims who suggest they are being wrongly targeted, denouncing this as “political correctness gone wrong”, arguing that Islamic extremism has to be closely monitored because people are “willing to die for the cause. If you carry on killing and committing acts of murder on our streets . . . you’re going to have to deal with the consequences of it,” he says. “If there hadn’t been these attacks, we wouldn’t be here.”

However, Khan is surprisingly ambivalent about Prevent as a whole, and is happy to discuss its weaknesses. He worries that sometimes, spending time with a client is giving them more professional respect than they deserve. “I’m thinking, ‘Why am I wasting this time with this guy because he’s a complete radical nutcase and I really need to tell him straight,’ ” he says.

Khan’s primary concern is that because engagement with Channel is voluntary, the most serious cases — those who are yet to commit a crime but are exhibiting violent extremist tendencies — are unlikely to accept help.

He repeats a criticism I also hear from human rights solicitors: children are sometimes being referred because they are easier to co-opt than the adults in their family. Khan tells me about a recent referral in which a young person was repeating worrying phrases learnt from his grandparents. “I said, ‘Refer the grandparents. They’re the ones who are telling him everything,’ ” he says. “That is the issue with the system — we’re going for people which are softer and not the hardened ones.”

The UK is not alone in running counter-radicalisation programmes, but its policies go further than most. Countries such as Norway and the Netherlands have similar strategies of intensive support offered by local agencies, but they do not impose a statutory reporting duty on their public officials.

Nick Wilkinson tells me he went to a counter-extremism conference in Brussels just after the legal duty was announced and “couldn’t believe how much hassle” he got from other national representatives, who denounced its heavy-handedness. “It was really shocking and surprising, the response coming back from these other European countries,” he recalls.

Within Britain, Prevent has been condemned by Muslim groups concerned about the implications of compulsory reporting for their community. Home Office figures show that while Channel cases are evenly split between Islamist and far-right extremism, the numbers of initial Prevent referrals are heavily weighted in favour of the former (44 per cent for Islamist extremism, compared with 18 per cent for far-right extremism).

Miqdaad Versi, a senior figure in the Muslim Council of Britain (MCB), tells me the requirement for teachers and even nursery staff to look for signs of extremism means that “many Muslim children . . . risk growing up being seen as potential security threats and feeling they may be treated differently due to their faith”.

I don’t think [Parsons Green] was a systematic failure of Prevent at all. It was a failure locally

Versi draws attention to the recent case of an eight-year-old boy who was reported to have been questioned by counter-terrorism officers under Prevent without his parents being present.

“He was apparently asked about Islam, the mosque he attends, if he prays and his views on other faiths. It is understandable why this child, his family and the local communities will lose faith in a system where such questions are deemed appropriate,” he says.

The MCB also has concerns about how Prevent referrals — even those found to be without basis — “may create a false picture of a young child, potentially impacting their life chances or giving the impression of the child being a potential security risk in the future”.

Education bodies have now overtaken police as the most prolific source of Prevent referrals, accounting for a third of the total. Just over half of those referred were aged 20 or under, according to the most recent data. The councils I spoke to assured me that the names of Prevent clients are only passed on to police if a formal referral is deemed appropriate. However, all names are kept on a council database, subject to strict data protection rules.

Police alongside groups of far-right protesters marching through Dover in Kent, April 2 2016 © Justin Tallis/AFP/Getty Images

Independent research has cast further doubt on Prevent’s approach to Muslims. In 2016, parliament’s Home Affairs Committee branded the programme “toxic” because of the strength of opposition from Muslim groups, and called for it to be reformed and renamed.

The same year, a study by the New York-based Open Society Foundations argued that the programme presented a “serious risk” of human rights violations and said the concept of targeting pre-criminal extremism was “fundamentally flawed”. A few months ago, the UN’s special rapporteur on racism suggested the entire scheme should be suspended while the government investigated its impact on the Muslim community.

There are more specific criticisms too. A report into the terrorist attacks of 2017 by cross-party MPs on the Intelligence and Security Committee (ISC) raised multiple concerns about the management of the Parsons Green case.

“The litany of errors that resulted in Hassan’s attack-planning passing unnoticed, despite his participation in the Channel programme, highlights deep-rooted issues in the Prevent strand of [counter-terrorism strategy],” the ISC concluded. The committee also denounced the Home Office’s response to its queries as “weak, lacking in clarity and unacceptable in light of the seriousness of the failings”.

Ben Wallace, the Home Office minister responsible for Prevent, tells me he disagrees with the ISC. “They never asked me for my view, they never interviewed me,” he says. “I don’t think it was a systematic failure of Prevent at all. I think it was a failure locally to do what they were supposed to do, and that’s being rectified.”

The most damning evaluation is an unpublished report by the Behavioural Insights Team (BIT), a company part-owned by the government, which applies the principles of behavioural science to public policy. BIT studied 33 deradicalisation programmes in schools, youth centres, sports clubs and English-language classes across the UK. Of these, only two were found to be effective.

Presenting their findings to a group of police officers last year, researchers said that while the programmes were based on good intentions, they were not underpinned by any evidence-based research, adding that ineffective programmes had been let down by facilitators who were “uncomfortable dealing with sensitive topics” and teachers who were “afraid to bring up race or religion with their students”.

The behavioural psychologists complained they had found “little in terms of robust evaluation frameworks”, suggesting the reported success rates of more than 90 per cent in some programmes were “not believable”, and likely to be the result of intervention providers marking their own projects. Their central criticism was that deradicalisation programmes were not backed up by a “sufficiently robust standard of evidence”.

Neither the Behavioural Insights Team nor the Home Office was prepared to give me a full copy of the study, so the comments above are based on a report of the lecture that appeared in Police Professional, a trade publication. Peter Neyroud, a former chief constable who attended the event, says the Home Office deserves credit for allowing its programmes to be evaluated, but says it is imperative that the research is published.

He is now overseeing a much larger study into evidence for deradicalisation programmes on behalf of the “five eyes” intelligence alliance comprising Australia, Canada, New Zealand, the UK and the US. “Britain is not the only place asking these questions,” he says. “All these countries need to know how to make it work.”

Wallace insists that the BIT report only considered a “tiny amount” of Prevent’s work, and didn’t cover the harder end of Channel, just a few projects at community level. When I ask where the evidence base is for Prevent, he claims his evidence is the results themselves.

What is pre-crime? It really does amount to . . . thought policing

“[In the past two years], 500 people have been through the Channel process who we are no longer worried about,” he says. “That’s 500 potential people that could have caused harm on our streets, and very serious harm. That is, to me . . . some good evidence. I think my evidence base is that I do believe it is working. It, overall, is working. It is producing some good results. It’s finding people that need safeguarding.”

Amrit Singh, a human rights lawyer and head of national security and counter-terrorism at the Open Society Foundations, disagrees. She says the Home Office has no solid empirical grounding for its ventures in deradicalisation, as there is no way to predict who is going to become the next terrorist.

She argues that there are more than enough provisions in the law for criminal prosecutions of terrorists once crimes have been committed. By pre-empting that, Singh says the government has unleashed a “mass of unscientific indicators” into this area of policy, “and with what results?”

Her conclusion — after months spent evaluating the programme — is that by imposing a statutory duty on its public servants, the UK has strayed further than any other country into surveillance of people’s everyday lives, with little justification.

Singh compares the notion of pre-criminal intervention to the movie Minority Report, in which police deploy “psychic technology” to apprehend murderers before they commit their crimes. “What is pre-crime, and how do you determine that somebody is going to commit a crime before they have even formed an intent?” she asks. “It really does amount to . . . thought policing.”

Sixteen years after it began, Prevent remains one of the British government’s most polarising policies. Budgets have more than doubled from about £20m a year in the first few years to £45.5m in the past 12 months. Recognising the need for transparency, the Home Office has embarked on a drive to explain Prevent better — publishing statistics on referrals, and telling the stories of the programme’s successes.

The promised review may temporarily quieten critics, but examples of Prevent’s weaknesses are all too easy to find. Last month, it emerged through a court hearing that Lewis Ludlow, a 27-year-old Islamic convert from Rochester, Kent, had been engaging with Prevent to distract from what police called “hostile” activities.

The prosecution revealed that one of Ludlow’s terror contacts advised him to “be polite” with Prevent personnel, telling him: “Even if u don’t believe it, fake it.” Ludlow, a former postman, was later found to have scoped out sites for an attack on Oxford Street just hours after a session with his Prevent mentor.

I would present Prevent as something that’s there to help you. You can walk away, whenever

Wallace is frank about the difficulties. “It will always be a moving, living thing, Prevent, and it will not always be 100 per cent successful,” he says. “Not everyone will either take the assistance or, indeed, respond to it. But show me any government that promises a 100 per cent safeguarding success rate.”

The rising threat from the far-right poses a new and daunting challenge. Mark Rowley, former head of counter-terrorism for Scotland Yard, warned last year that the UK had not yet “woken up” to the risks of far-right extremism, allowing dangerous groups the “scope to get stronger”.

A shrine for the MP Jo Cox, who was murdered by a constituent with far-right views in June 2016 © Oli Scarff/AFP/Getty Images

The murder in 2016 of Labour MP Jo Cox by Thomas Mair, a loner with long-held neo-Nazi beliefs, shows there will always be those who are beyond the reach of Prevent, and who do not receive help before it is too late.

Even with the Home Office’s co-operation, it is hard to identify individuals who are willing to talk about positive experiences with Prevent. It is not until I find Ali, a Channel recipient, that I speak to someone whose life has been changed for the better by the programme.

He was referred, aged 15, by a teacher, who realised Ali was being influenced by an extremist Islamist preacher. He was assigned a mentor who would take him for coffee and they would discuss politics, religion and being a Muslim in Britain. A few weeks in, Ali heard that one of his school friends who had gone to Syria to fight had been killed. He realised he was scared at the prospect of such violence, and began talking to his mentor about staying in education, getting a degree and perhaps even considering a civil service career.

Several years on, Ali’s enthusiasm for Prevent borders on evangelism. He expresses a genuine gratitude for the teacher who referred him and the specialist assigned to coach him. He believes those who criticise Prevent simply don’t understand it: “They make it out to be a government programme that is out there to catch people and stuff but I would present it more as something that’s there to help you,” he says. “Nothing is forced upon you and you can walk away, whenever.”

He discusses his experiences evenly, and chats enthusiastically about his Master’s thesis, his interest in geopolitics and his plans for the future. But when I ask what might have happened if he had not been referred to Prevent, there is a catch in his voice.

“I think I would have gone down a bad road,” he says, and there is a long pause while he thinks about the life not lived. “Who knows?” he says quietly. “Who knows?”

Helen Warrell is the FT’s public policy correspondent. Some names and details of Prevent referrals in this piece have been changed at the Home Office’s request

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