A photograph of Aaron Collis regularly appeared in the press while he was on trial. It showed a young man in a crowd of friends, whose faces have been pixelated to preserve their anonymity, and it appears to capture a moment of celebration. The group are bunched together, arms in the air, all wearing the same white shirts and roughly knotted blue-and-red striped ties. They could be in school uniform, or party costume. Collis is looking up at the camera, a wide smile exposing a top row of pointed teeth. The photo was taken in a dark room with the flash on, so his face is starkly lit and every pock and mole visible. His eyes are narrowed to slits and his nose seems abnormally large. You can see why the image was used: Collis’s face is distorted, and disturbing. It is a fitting portrait of a paedophile.

In October 2009, Collis, then 24 years old, was convicted of committing 11 offences of sexual abuse against five children. He was given an indeterminate sentence, with a minimum five-year term. In March 2012, he was sentenced to a further five years, to run concurrently, after admitting to offences against another 13 children. The youngest of his victims was 18 months old. At the original sentencing, the judge, Gareth Hawkesworth, told Collis that he would only be released from prison once he no longer posed a threat to “life and limb”. “The hurt you have done to these young children and their families is incalculable,” he said. “These were evil and repulsive offences which any right-minded member of society can barely comprehend.”

After sentencing, Collis went to prison at HMP Parkhurst, on the Isle of Wight. From there he contributed to the February 2014 issue of Inside Time, the prisoners’ newspaper: “I am a 28-year-old sex offender who has always openly admitted his crimes from the word go,” he wrote. “I hate what I have done and for four-and-a-half years now I’ve been in the prison system trying to find a ‘cure’ for the incurable. I found a solution a while back and have been exploring it ever since, but for some reason I am finding it nearly impossible to convince people that chemical castration is the best thing for me.” Collis said he had appealed to doctors, nurses and psychologists – but had so far failed to gain access to the medication he desired. “I thought they would jump at the chance to take away my sex drive, but I was very wrong. They all seem to be trying to talk me out of it, telling me I’m young and it’s not necessary. Well, I’m sorry, but it’s my body and my messed-up brain which is dangerous and this is my decision.”

Collis’s plea for help to “take away” his sex drive raises a number of uncomfortable questions. Paedophiles occupy an unambiguous position in society: they are the lowest of the low, the authors of unspeakable crimes – not only “evil and repulsive”, as the judge said, but incomprehensible. For some, the very idea of rehabilitation is questionable: do these individuals deserve to be helped? Can someone who has abused a child be forgiven or changed? Most uncomfortable of all, does a medical intervention – in the form of drugs that eliminate sexual desire – imply that there is a “cure”, that paedophilia is a sickness rather than the worst possible crime?

Last summer, after coming across Collis’s letter to Inside Time, I wrote to him in prison. Our correspondence lasted for several months and raised its own concerns. To what extent could Collis’s version of himself be trusted? He admitted that though he owned up to his crimes, he had “fabricated all sorts of rubbish in police interviews”. But writing to him was part of an attempt to answer two questions that, given the disgust that naturally attaches to these crimes, have become difficult even to ask: what makes someone a paedophile? And what should we, as a society, do about them?

When Collis arrived at Parkhurst in 2009, he took part in the Sex Offenders Treatment Programme (SOTP) – courses devised by psychologists and run to minimise an inmate’s risk, and help them develop healthy sexual behaviours. But he found the programme ineffective. “I learned absolutely nothing on the SOTP,” he wrote in one of his first letters to me, last July. “All they do is overanalyse irrelevant parts of our lives, and make up random ‘risk factors’ to work on.” Over his years of incarceration Collis said he had met hundreds of sex offenders who had taken part in the programme and got good reports. In his view, they were playing the system. “Not one of them was honest.”

Collis traced his attraction to children back to puberty. “To begin with I was hoping it was just a phase I was going through,” he wrote. “I soon realised that I was a paedophile and that was never going to change.” His early childhood had been happy, he said, but at the age of seven he was abused by a stranger and then by a teacher. At school he was bullied and became socially isolated. As he went through his teenage years, he felt unable to form relationships with his peers and so befriended younger children. From the age of 14, he knew that his feelings towards these children were inappropriate, and sexual.

Not long after his arrival in prison, Collis watched an episode of ITV’s This Morning in which a convicted rapist talked about being “chemically castrated”. The man said he had been prescribed a course of anti-libidinal drugs that had drastically reduced his sex drive. Then Collis met a fellow inmate and sex offender who had been in and out of prison for 20 years. “He had done all the Mickey Mouse courses,” Collis wrote. After reoffending and being sectioned, the inmate was sent to hospital and later prescribed medication: “And he has never thought about sex since. It’s no longer part of his life.”

Collis began to research the treatment and decided that it was essential to his rehabilitation. He believes he was born a paedophile, and that his attraction to children is unchangeable. “I did NOT wake up one morning and decide my sexual preference. I am sexually attracted to little girls and have absolutely no interest in sex with adults. I’ve only ever done stuff with adults in order to fit in with what’s ‘normal’.” For Collis, therefore, it became a question of how to control this desire and render himself incapable of reoffending.

To begin with I was hoping it was just a phase. I soon realised I was a paedophile and that was never going to change

Collis said he repeatedly put forward requests for assessment to doctors, psychologists and prison officers, but found his efforts thwarted. “I kept getting passed on to different departments; no one wanted to take responsibility,” he wrote. He became frustrated, and so wrote his letter to Inside Time: “For some reason I am finding it nearly impossible to convince people that chemical castration is the best thing for me … WHY?”

* * *

From April this year, a new programme of chemical treatment will be rolled out across the country. For the first time on a national scale, anti-libidinal medication will be made accessible to sex offenders in prisons and through probation services. It has taken a while to get to this point. Don Grubin, a forensic psychiatrist who has spent most of his long career treating sex offenders in Newcastle, first proposed such a programme back in 2007. It was welcomed by John Reid, then home secretary, who “got the horses running”, according to Grubin.

In 2008, a pilot project was established at HMP Whatton, a prison for sex offenders in Nottinghamshire, and more than 100 inmates and former inmates on parole have since been prescribed anti-libidinal medication. Protracted negotiations followed about how the programme could be scaled up, from an individual project to a nationwide scheme, and about how it would be run and financed. Now, a new national network of clinics will finally be established. Grubin is acting as an adviser, and the programme will be funded and co-managed by NHS England and the National Offender Management System as part of the “Offender Personality Disorder Pathway”. Forensic psychologist Sarah Skett, who is leading the initiative for the NHS, described its aims as twofold: to give offenders more control over obsessive sexual thoughts and feelings, and to reduce the risk to the public.

Grubin is a short, wiry-haired man, jovial and pragmatic by nature, with an undiluted New Jersey accent despite half a lifetime spent in the north of England. He grew up in Short Hills, a quiet commuter town an hour west of New York City, and was the son of the local doctor. After spending a year of his undergraduate degree at Oxford University, Grubin decided to stay in the UK, began his medical training in 1980, and then, in 1988, decided to specialise in forensic psychiatry, working with mentally disordered offenders. “I always thought that minds were more interesting than stomachs or bones,” he told me.

Grubin never set out to work with sex offenders. Early in his career, a colleague asked him to help out on a research project in Maidstone prison in Kent, working with offenders in denial. This led to another research post, and soon enough he had established himself among prison psychologists as a rare psychiatrist willing to work with sex offenders.

“Many psychiatrists aren’t interested in it,” he said. Many, too, find it morally uncomfortable, believing that psychiatrists should be treating the mentally ill, not criminals. And some do not want to take the risk: what if an offender you treated subsequently committed another crime? Over the years, Grubin became known as an expert on chemical treatment, partly because he was one of few psychiatrists willing to prescribe to offenders. (“The only bloody one!”, as one ex-probation officer put it to me.) If a sex offender was unable to access treatment in prison, he was often referred to Grubin who, if too far away to treat them himself, would try to find a psychiatrist nearby to take on the case. Some had little experience with sex offenders, and he was never sure of the outcomes of treatment. “It was very hit-and-miss,” said Grubin.

The plan to make chemical treatment nationally available was born of necessity: Grubin’s one-man referral agency was not sustainable in the long term. But it was also a logical product of his bracingly practical assessment of the problem of sexual offending. An individual sex offence, Grubin told me, was estimated by the Home Office in 2010 as costing society £36,952 – taking into account the costs of police investigation, judicial proceedings and any medical treatment the victim requires, as well as the cost of the profound and often long‑term emotional impact on the victim, and their “lost output”. By comparison, a year’s worth of sex-drive-reducing selective serotonin reuptake inhibitors (SSRIs) costs around £50, while more intensive anti-androgen medication costs between £300 and £2,000 a year, depending on how it is administered. As Grubin put it: “You don’t need to prevent very many offences to get your money’s worth.”

* * *

In recent years, Britain appears to have been gradually and painfully unveiling itself as a nation of paedophiles: Jimmy Savile, Stuart Hall, Yewtree, Rotherham, Rochdale, the ongoing and controversial investigations into an alleged Westminster-based ring of child abusers. Last week, Dame Janet Smith’s review of the BBC’s mishandling of the Savile case reopened the ferocious debate about this country’s apparently historic inability to prevent these crimes. The ongoing Independent Inquiry into Child Sexual Abuse, established in March last year, is examining what appear to be chronic failures in child protection across almost all the major public institutions in the country: schools, hospitals, the armed forces, the BBC, religious organisations, charities, the police. There is a sense, particularly in a panic‑hungry media, that Britain is in the grip of an epidemic, a country riddled with abuse.

The actual extent of the problem is hard to pin down. Last year, the National Crime Agency (NCA) estimated that one in 35, or nearly 3%, of men in Britain was a “potential paedophile”. Figures released by 33 different police forces last year showed that there had been a 60% increase in reported child sexual abuse since 2011. The NSPCC, meanwhile, says that one in 20 children in the UK have been sexually abused, 90% by someone they know and over half by a member of their family. “The reality,” said deputy director of the NCA, Phil Gormley, in media interviews, “is that we are all living not far away from one.”

The reality, arguably, is more complicated – and an evaluation of the risk depends on how you define paedophilia. The assumption, made frequently in the media, is that anyone who abuses a child is a paedophile. But clinicians use a more stringent definition: someone whose primary sexual interest is in prepubescent children. Using that definition, the Canadian forensic psychologist Michael Seto, who has authored multiple studies of paedophilia, has estimated that fewer than 1% of the population are paedophiles. (This is based on small-scale surveys: a lack of large epidemiological studies mean that there is no accurate prevalence rate.) The number of individuals viewing child abuse images online has risen, but this is not necessarily synonymous with the number of abusing paedophiles. In a paper published in 2011, Seto examined the recidivism data for 2,630 online offenders and revealed that 2% had gone on to commit “contact” sexual abuse.

Beyond the basic definition, experts diverge in their explanation of paedophilia and its causes. Almost every psychiatrist, psychologist, probation worker and sexologist I spoke to conceptualised the problem in a slightly different way. Crime, illness, sexual orientation – all can apply. The debate can perhaps be boiled down to a question: are you born a paedophile, or do you become one?

Figures from 33 police forces last year showed there had been a 60% increase in reported child sexual abuse since 2011

Many experts support Aaron Collis’s self-assessment, that paedophilia is an unchangeable sexual preference. In a 2012 paper, Seto examined three criteria – age of onset, sexual and romantic behaviour, and stability over time. In a number of studies, a significant proportion of paedophiles admitted to first experiencing attraction towards children before they had reached adulthood themselves. Many described their feelings for children as being driven by emotional need as well as sexual desire. As for stability over time, most clinicians agreed that paedophilia had “a lifelong course”: a true paedophile will always be attracted to children. “I am certainly of the view,” Seto told me, “that paedophilia can be thought of as a sexual orientation.”

Brain-imaging studies have supported this idea. James Cantor, a psychiatry professor at the University of Toronto, has examined hundreds of MRI scans of the brains of paedophiles, and found that they are statistically more likely to be left-handed, shorter than average, and have a significantly lower density of white matter, the brain’s connective tissue. “The point that’s important for society is that paedophilia is in the brain at all, and that the person didn’t choose it,” Cantor told me. “As far as we can tell, they were born with it.” (Not that this, he emphasised, should excuse their crimes.)

Heather Wood – a psychotherapist and psychologist at the Portman Clinic in London, which specialises in treating violent and sexual offenders – prefers to think of paedophilia as a more developmental problem. Drawing on psychoanalysis, she described how she studies an offender’s personal history to try and understand why they developed a sexual attraction to children at a particular point in their life. “In the normal course of development,” Wood said, “when you’re 11, you fancy 11-year-olds, and when you’re 15, you fancy 15-year-olds, and as you mature, the age of the persons to whom you’re attracted develops. What we see in some of the patients is that they get stuck in adolescence, so at 11 it’s 11-year-olds and at 15 it’s 11-year-olds, and at 18 it’s 11-year-olds. Their sexual interest doesn’t mature.”

In the 2013 edition of the Diagnostic and Statistical Manual of Mental Disorders (DSM-5), the American psychiatric classification system used around the world, paedophilia is classed as a “paraphilic disorder” – an atypical sexual interest that either causes distress to the person with the disorder, or makes them a threat to others. Some believe that paedophilia should not be in the DSM at all, such as sexologist Richard Green, who successfully campaigned for homosexuality to be removed from the DSM in 1972, and argued in a controversial 2002 paper (“Is paedophilia a mental disorder?”) that paedophilia should also be removed. In the paper, Green included an exotic cross-continent tour of places where child-adult sex had historically been the norm (Hawaii, Tahiti, New Guinea), and reminded readers that for three centuries, until the Victorian era, the age of consent in England had been 10. “This was not in a period contemporaneous with Cromagnon man,” he wrote, “but continued to within 38 years of World War I.” Green’s argument did not suggest that sex with children was acceptable, or should be legal, but that the desire to have it did not necessarily constitute a mental disorder. He cited previous research, which had evaluated “non-prisoner, non-patient paedophiles” – that is, non-abusing, mentally well individuals who were primarily sexually attracted to children. After examining their scores on major personality dimensions, including neuroticism and psychoticism, Green found that it striking “how normal the paedophiles appear to be”.

For many of those working directly with sex offenders, the definitional wrestling around paedophilia is beside the point: the urgent societal problem is the protection of children. “Often people will come to see me and say I’ve offended and I just want to know why, I want to know why I did it,” said Grubin. “And my response is, that’s a luxury. The first thing is to stop you doing it again.”

Illustration by Pete Gamlen

* * *

Once, we cut their balls off. The first recorded castration for psychiatric reasons was performed in 1892 in Zurich, Switzerland, by the psychiatrist August Forel. In his 1906 book, Die Sexuelle Frage, or The Sexual Question, Forel admitted to having “castrated a veritable monster afflicted with constitutional mental disorders, taking advantage of the fact that he himself requested this operation to relieve him of pain in his seminal vesicles, but with the chief object of preventing the production of unfortunate children tainted with his hereditary complaint”. Forel, a pioneer in the field of sexual behaviour, also had a tendency towards eugenicist thinking. (He also admitted to “castrating” women, including “a young hysterical girl of 14, whose mother and grandmother were both prostitutes, and who had already begun to have intercourse with all the urchins in the street”.)

The procedure soon became popular across Europe. Denmark legalised surgical castration in 1929 and Germany, Norway, Finland, Estonia, Iceland, Latvia and Sweden followed relatively swiftly. The scale of its use varied: academic studies suggest that since 1910, in the Zurich region of Switzerland alone, 10,000 patients were castrated for various psychiatric reasons. Some 1,100 cases of physical castration were recorded in Denmark until they abandoned the practice in the 1970s. As recently as 2012, it was reported by the BBC and others that up to five voluntary castrations were taking place in Germany every year. The only European country that still uses surgical castration with any regularity is the Czech Republic, where 94 operations have been performed on consenting patients since 1999. Opposition, however, has mounted. In 2009, the Council of Europe’s Committee for the Prevention of Torture heavily criticised the Czech Republic’s continuing use of the procedure: “Surgical castration is a mutilating, irreversible intervention and cannot be considered as a medical necessity in the context of the treatment of sex offenders.”

Today, treatment typically consists of drugs or psychological therapy, often both. First, an individual has to be assessed. Don Grubin likes to say that there are two types of sex offenders. “Do you remember The Good, The Bad and The Ugly?” He recounted a scene where Clint Eastwood is attacked by a man coming into his bedroom. Eastwood kills him, then turns to find two more sitting in the window, guns pointed. “And Clint says, ‘There are two sorts of cowboys, the ones that come up the stairs and the ones that come through the window.’ With sex offenders it’s the same sort of thing – there are Those working with you and those working against you.”

The first challenge, then, is to work out what you are dealing with. When Grubin meets a sex offender for the first time, he uses a system he calls the four-box method, examining sexual arousal, antisocial attitudes, emotional self-regulation and “life management”. Grubin only gets worried if a case ticks more than one of the four boxes. “Someone who is strongly sexually attracted to kids, but sees sex with children as harmful; doesn’t believe in rule breaking; doesn’t, when they get depressed, see that as an excuse to harm: if you don’t have any of those other boxes firing then you’re not going to act on that sexual arousal,” said Grubin. “But if you do, then you become a risk to kids.”

The only European country that still uses surgical castration with any regularity is the Czech Republic

Medication falls into two categories: SSRIs and anti-androgens. SSRIs are a type of anti-depressant that dampen libido. They are the more commonly prescribed treatment, being both less invasive and much cheaper than the alternative. According to a paper by two leading Israeli psychiatrists, Ariel Rosler and Eliezer Witztum, SSRIs appeared to be effective “solely in men with a definite obsessive compulsive disorder component”. Anti-androgens, meanwhile, have a more drastic effect. The drugs, taken as tablets or by injection, block the production of testosterone, one of a group of male hormones collectively known as androgens. They are proven to work, although there are side-effects – including osteoporosis and hot flushes. (Some men, one ex-probation worker told me, grow breasts while undergoing treatment.) Rosler demonstrated the effect of a particular anti-androgen, called triptorelin, which was prescribed over 15 years to 100 men with severe paraphilias (80 of which were paedophiles or non-paedophilic child abusers). All of the men experienced a decrease in their abnormal sexual fantasies and desires, and, while they took the drug, exhibited no abnormal sexual behaviours.

Clinical reality is a little more complicated. “There’s no pretence that the treatment is somehow going to cure them of paedophilia,” Grubin told me. “I think there is an acceptance now that you are not going to be able to change very easily the direction of someone’s arousal.” Grubin estimates that medication is only suitable for about 5% of sex offenders – those who are sexually preoccupied to the extent that they cannot think about anything else, and are not able to control their sexual urges. As Sarah Skett from the NHS put it: “The meds only take you so far. The evidence is clear that the best treatment for sex offending is psychologically based. What the medication does is help people have a little bit of control, which then allows them to access that treatment.”

Even then, the drugs are likely to be a temporary fix: treatment is voluntary in the UK and even the worst offender can choose to stop taking the medication at any point. In the Rosler study of 100 sex offenders, 10 of the men who quit treatment for more than six months reoffended. Other countries – Poland, South Korea, Moldova, certain US states – take a different approach, including medication as a mandatory part of a prison sentence or release package.

But enforced chemical treatment is unlikely to occur in the UK. For a start, it goes against the principles of many doctors.

As Grubin said: “You’re looking to the benefit of that individual, no matter how awful some of the things they’ve done are.” It’s why he dislikes the term chemical castration: it sounds more like punishment than treatment. “As a doctor,” said Grubin, “the person that you’re treating is your patient. Society is not your patient.”

* * *

Aaron Collis was a prompt and careful correspondent. In his letters, he wrote in a neat, even script on the lined prison paper. If he made a mistake, he used correction fluid to conceal it. In one letter, sent in August last year, he told me he had been diagnosed with various personality disorders: “borderline personality disorder (emotionally unstable), obsessive-compulsive personality disorder, dependent personality disorder, with significant narcissistic histrionic and antisocial traits”. (He also offered a caveat: “My personality disorders are NOT an excuse for my crimes.”) As a result, he had been prescribed an SSRI that had helped to reduce his sex drive, but he was still hoping for further treatment. When I asked him why he thought he had previously been refused medication, he said that he had been told there was no evidence it would reduce his risk: “They say that the desire would still be there and I would still get emotionally obsessed with children like I used to.”

Drugs are only likely to be a temporary fix: ­treatment is voluntary and even the worst offender can choose to stop

Drugs can reduce the sexual urge, but their effects are limited when it comes to complex emotional problems. Take the case of Tim – not his real name – who I met one afternoon last summer in Kent. Tim was a large man, bald, in tracksuit bottoms and a T-shirt, who had spent several years in prison for sex offences, and now spent his days wandering round the charity shops of his local town and helping his elderly neighbours with their gardening. Once a week he worked at the hostel where he had lived after being released from prison, for which he received payment in the form of Iceland vouchers. He was still in touch with only one of his siblings, though if he happened to meet a family member while out shopping, they might say hello to him.

Tim had started offending as a young man. His behaviour, he said, was partly a consequence of his inability to have a relationship with a woman and the bullying he experienced from younger colleagues at the place where he worked. “I felt, ‘Why me?’ he said, ‘Why are they picking on me?’ When I left work one day I went and did something sexual. Someone saw me. My ID was given. That time I got let go.” Tim started out exposing himself to women, then looking through their windows. “Then I was told: ‘How long will it be before you touch somebody or rape somebody?’ They were seeing a pattern.” After one of his offences, Tim was referred by a magistrate to see a psychiatrist who prescribed an anti-androgen. He took the medication a few times – by injection in his stomach – but then stopped. “It didn’t work,” he said. “I still went out and offended. It reduced the drive. But my mind … back then, I do believe it was my mind telling me to carry on. I wasn’t doing it so much when I had the injection, but I still had the thoughts in my head of going out doing it. And sometimes those thoughts got that powerful. I tried to stop myself.”

Not long afterwards, Tim started abusing a 15-year-old female relative, and it was this crime that led to his arrest and imprisonment for four years. He never abused a prepubescent child, and resents being labelled a paedophile. “If you say to people, ‘I’m on the sex offenders register,’ straight away they think you’re a paedophile. That’s not the case,” he said. “I wasn’t attracted to young children.” While in prison, he took part in the SOTP courses and – unlike Aaron Collis – said he found them transformative. The courses helped him to see why he had offended: he was lonely, isolated, angry, resentful of these colleagues who were bullying him. He identified certain triggers, too, or “risk factors”, as the terminology goes: being on his own in secluded places after dark, watching too much porn. “Now I don’t have any of that.”

Tim’s so far successful rehabilitation has been in part thanks to the support of an organisation named Circles UK. Set up in 2002 and funded by the police and probation services, Circles recruits volunteers to support a sex offender on release from prison. A group – or circle – of these volunteers then meet with the ex-offender weekly for a year to 18 months, in the hope that by providing regular social contact they will counter the isolation sex offenders often experience after release and prevent reoffending. There is no precise way of evaluating the impact of their work but the 5% sexual reoffending rate (nine out of 181 Circles cases, according to the organisation’s most recent annual report) is markedly lower than the national rate of 26%. “Giving people hope for the future is absolutely key to people turning their lives around,” said Jan Thompson, a Circles volunteer coordinator for the south-east of England. “If you make people feel that they’re on the outside and there’s no way back, then there is no incentive for them to change. That is the reality that for some people is unpalatable.”

To access Circles, or the new network of clinics, a person must be in prison or on probation. They have to commit a crime, in a sense, to get help. What about those who have not actually abused yet? At present, the best preemptive option in this country is a confidential helpline and email service for people worried about their behaviour or desires, called Stop it Now!, run by the Lucy Faithfull Foundation. Callers are not required to reveal their identities, but if they do, and appear to be putting a child at risk or admit to an abuse, the charity is required to notify the police. So are doctors, if, for example, a patient admits to looking at child pornography. “I think that’s wrong,” Don Grubin once said to me. “How are they ever going to get any help?”

In Germany, by contrast, a programme called “Project Dunkelfeld” runs clinics across the country offering confidential treatment to anyone experiencing attraction to children, even if they have committed an abuse. This would not happen in Britain, where the rights of a victim understandably come before those of an offender. But then it comes back to the unmeasurable – the potential offender, the man attracted to children who is yet to act. How many offences might be prevented if he could rapidly access treatment?

* * *

In August last year, the Ministry of Justice published figures showing a that sexual offender convictions had reached a 10-year high and that sentences had risen on average by 4.5 months. “These figures show that sex offenders are receiving harsher punishment than ever before for their appalling crimes,” said the undersecretary of state for prisons, probation and rehabilitation, Andrew Selous, when the statistics were released. But, despite the political support for a hardline custodial approach, the average sentence for a sex offender is relatively short: five years and three months.

Even paedophiles with long and horrifying records, like Aaron Collis, are eventually let out of prison. “I’m now 30 years old and I have about 20 months left on my tariff,” he wrote in a letter sent in July. “I’m confident I will be out by the time I’m 35 years old. I will still be young, but will I be rehabilitated?” For someone like Collis, rehabilitation – whatever form the treatment takes – will be a management of desire, not an eradication. There is no cure. However you define or explain paedophilia, the more pressing concern, therefore, is how a society responds to the problem, and protects its children.

Collis’s last few letters to me, towards the end of last year and early this year, were relatively short. Sometimes they were written simply to check I had received a previous letter, if I had not responded quickly enough. His tone varied. One, written last September, seemed angry and increasingly lacking in remorse, as though he had lost patience with even the possibility of rehabilitation. “What I’ve told you is my version of how things have gone to the best of my knowledge,” he wrote. “I’m a lost cause. There’s NO WAY I’m ever going to stop being a paedo. That’s who I am and I refuse to be in any way ashamed of who I am. I don’t give a shit what anybody thinks. I’ve done my time, and fuck everybody who turned their backs on me.” He’d signed off the letter with his signature, and then a block capital inscription: “THE BEAST FROM THE EAST”.

A few weeks later, he wrote again, apologising for the aggressive tone of his previous letter. “I’ve done all I can possibly do in prison,” he said in his final letter, in January this year, “and with a year left on my tariff, it’s about time I start looking to the future – beyond prison! I’ve done my time now, I’ve been adequately punished. It’s now time to push for the right help in order to set me up for a good, healthy, offence‑free future.” At the end of the paragraph, he had drawn a smiley face.

Main illustration by Pete Gamlen

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• This article was amended on 9 March 2016 to make clear that the organisation Stop it Now! is only required to report the identities of callers to the police if the caller chooses to give identifying information.