Since Stinson Hunter declared war on sex abusers in his bedroom back in 2009, a cluster of vigilante groups have sprung up, dedicated to snaring Britain's paedophiles and circumventing the country's police force in the process.
Groups such as Letzgo Hunting and the Online Predator Investigation Team (OPIT) have joined the fight, employing sophisticated tactics and resources to track and catch abusers. It can resemble a 21st-century version of fox hunting, except this time the public has no sympathy for the prey.
The latest group to hit the headlines is the grandiose and sinister-sounding Dark Justice, a two-man operation based in Newcastle whose stings have yielded seven arrests in just four months. Last week, 45-year-old Roger Lee was jailed due largely to the evidence the pair of vigilantes had gathered against him.
It was a classic sting by the group, who used a fake online identity to lure Lee into arranging a meeting with someone he believed to be an underage girl. But when the man turned up to meet his potential victim in Newcastle, he was greeted by two men with a video camera. The predator had become prey.
Transcripts of explicit online conversations between Lee and Dark Justice showed he was aware his potential victim was underage and that he also initiated the meeting in Newcastle. Video evidence of the encounter with Dark Justice sealed Lee's conviction.
The whole procedure is clearly very complex and time-consuming, so what drives the orchestrators? What compels them to spend hours preparing these stings without any financial reward?
Speaking to IBTimes UK under condition of anonymity, the two Dark Justice founders reveal that, although they don't have children themselves, there is a personal element to their crusade. One of them says: "When I moved to Newcastle, there was an incident outside my house when one guy tried to snatch a child. It pushed us to want to do it."
There is also, apparently, a wider objective at work here. The founders say their real motivation "is to get the police more funding to do these sting operations, because the government funding has been cut".
At present, the British authorities are grudging in their tolerance of the vigilantes fighting online paedophilia. However, the Dark Justice co-founders insist they perform a valid and important role, and are not treading on the toes of the authorities.
"This Roger guy... if it wasn't us he was talking to, he would have talked to another girl," says one of the founders. "He admitted he liked younger girls.
"So at least he was talking to two fully grown men who have now got him on a sex offender's register for life. Now he's on the register, the chances of him doing this kind of thing again are going to be slim, considering the judge said that if he ever goes in front of the court again for that type of crime, he's going down for life."
'Nine times out of 10 they get sexual almost immediately'
The two men snare victims by going on a site and setting up a profile, with a picture of a "decoy" – one of their friends, or a volunteer, who has consented to the use of their image online. They claim they never set out to lure people under false pretenses.
"When people message us, within the first three minutes we will always say: 'I'm 14 years of age, I'm just on here to make friends,'" one of the men says. "Then they start talking back and nine times out of 10 they start getting very sexual.
"We just set a profile up, I won't say the site, and within the first half an hour we've already got 15 people who are potentially wanting to meet; they've already broken that barrier of sexual contact.
"We had one who wanted to pay for us to come round while him and his mates played poker and serve drinks naked. He knew this was a 13-year-old girl. The person that we're talking too, literally at the moment, has said: 'When we meet, could you wear your school uniform so you can pretend you're my daughter?' It's accompanied by explicit pictures too."
The founders are adamant it is always their correspondent who suggests a meeting and they always tell them they are underage before it gets to this stage. "Obviously when they say they want to meet, we take over, and pick the location so then we know we can control that environment."
When they go and "meet" their contact "we will spot them and then, 10 minutes before we walk over towards them, we'll ring the police and let them know what's going on, so then if the police choose to turn up and arrest them then they can."
'It's like something off football factory'
Dark Justice claim a wide range of people have fallen for their stings - "ex-army, teachers, everything".
Sometimes the police turn up and arrest the suspect on the spot. But, whatever happens, the Dark Justice founders insist "we try to be as peaceful and as quiet as possible". They claim they never carry weapons and always wait for the police to make their arrests before posting video footage of their snares online, to avoid mob justice being meted out.
Yet, for all the group's claims that they approach each takedown with rigour and calculation, there is clearly an element of exhilaration, a sense of relish as they swoop in and spring the trap.
"It's sort of like something off football factory, one of the men says when we ask them how it feels. "It is an adrenaline rush, you don't know what's going to come out of it. You don't know if they're going to be violent, although we haven't had any violent ones yet."
According to Dark Justice, the police actually collaborate with them by giving them advice on safety.
One of the men says: "Obviously they take us a lot more seriously now, the first couple they didn't think that we'd pull it off, but over time we've proved ourselves. We're now going to the local police station and [when] we say it's Dark Justice, there's a response straightaway.
"The only thing they've told us is if we keep making noise they'll provide us with a first point of contact. If a crime gets reported they have to take it seriously."
Yet, for all this talk of helping the police, the group are unwilling to do what might seem the easiest option – jump the fence and don the uniform themselves.
"Becoming a police officer means we'd have to be governed by the red tape," one of the founders says. "That means you become the government's bitch. For them to even make a phone call they need permission. If they wanted to set up a profile they'd need lots of permissions."
'These groups get in the way, it shouldn't be like this'
There is certainly some evidence to support Dark Justice's argument, specifically their claim that the police are crippled by lack of money; funding cuts of 20% have made detecting would-be sex abusers much harder to do. Judging by the positive reception Dark Justice and other groups receive on social media, they also have lots of public support.
Yet vigilantism has run into problems previously. OPIT drove one man to the brink of suicide, while Stinson Hunter's TV documentary, The Paedophile Hunter, showed clearly that physical harm is a real threat when amateurs carry out DIY stings.
Legal professionals and support groups are certainly unconvinced about the merits of vigilantism in the fight against paedophiles.
"Many people get why these so-called vigilantes do it," says Pete Saunders, head of the National Association for People Abused in Childhood (APAC). "Police forces up and down the country are having their resources cut at a time when there is no cut in the number of offences being committed.
"[But] the police and the authorities should be given the resources to take down these criminals; it should not be left to these groups. We do not want groups doing this because it can get in the way of criminal prosecutions.
"It's so easy to say it [the vigilantes' work] is great but it should not be like this. If people ended up walking free because of well-meaning interference by vigilantes then that's extremely unhelpful."
Lawyer Peter Garsden, of the Association of Child Abuse Lawyers (ACAL), agreed the authorities lack the funds to tackle online paedophilia effectively. He said: "The issue is the resources the police need to police the internet in the way they would like.
"There are issues surrounding the use of the evidence collected by these groups. It's done by amateurs and not the professionals. The police always condemn it and say no one should take the law in to their own hands because it is very dangerous and could be badly wrong; they [groups] are playing with fire.
"The police adopt exactly the same tactics in the investigations they carry out by pretending to be 14-year-old girls. It's not that this method of evidence gathering is unacceptable, but the problem is if it not done properly it can be a waste of time, if gathered by an amateur and not a professional."
Garsden pointed out vigilante groups risk violating breach of the peace and committing assault if their sting goes wrong. Furthermore, they could jeopardise the health of a suspect who is mentally ill or suicidal.
However, Dark Justice insist they are doing nothing wrong and bristle at suggestions that they risk breaking the law with their strings.
One of the men says: "We don't try to arrest anyone, we don't assault anyone, we don't ever breach the peace, we try to be as peaceful and as quiet as possible. As for trespass, we always meet in a public place."
So, what do they say to people who criticise them? "Well if you read the press [about Roger Lee], they said it would have been a real victim if he hadn't been chatting to us. We stopped a child from potentially being abused. At the end of the day, if we take one of them off the street, everyone's winning, because it's one less to worry about."
It seems as though vigilante groups such as Dark Justice are symptoms of the problem of serious underfunding for tackling adults who use the web to groom and sexually abuse children in Britain.
"People need to go and look online and see the problem," says one of the Dark Justice pair when asked about the scale of the problem. "We didn't think it was going to be as bad as it was until we started doing it.
"Anyone who thinks it's not big is deluded, basically."