The face is pixelated, but the man’s stammered denials during an unexpected and unwanted meeting in a park make clear his state of mind. “You have arranged to meet her, go to a hotel and offer her sex,” says the accuser who confronts him from behind the camera. He brushes off the man’s protests. “Can I just explain, you haven’t been speaking to a 15-year-old girl, you have been speaking to me.”

This is the conclusion of an operation by Letzgo Hunting, a self-styled anonymous online group of “paedophile hunters” whose vigilante tactics have been criticised by senior police officers following the suicide of Gary Cleary, 29, from Leicestershire, after he was confronted by the group.

Letzgo Hunting expressed sympathy for the family but defended itself and said it would not change tactics after a man it accused of grooming a child over the internet was found hanged following his arrest by police.

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Members of the group – founded by a man who goes by the online name of “Scumm Buster” – pose as young girls on social networks and engage with adults who contact them for sex.

Members of the group – which was inspired by a US crime television series – arrange meetings and then film the encounters, or the chase if the unsuspecting target flees. The footage is then handed to the police and also shown online.

The group claims that it has led to at least 12 arrests, including that of Gary Cleary, who was found hanged several days later in May. A coroner last week recorded his death as suicide but did not refer to his encounter with the group.

Jim Gamble, the former head of the Child Exploitation and Online Protection Centre, said: “I can understand the frustration of people going online and taking part in vigilante behaviour, but it’s simply wrong.

“When police engage with a potential predator they will take into account the likelihood that person might become suicidal. Forces will have policies in place for that.”

Police warned that paedophiles could infiltrate such groups, covert police operations could be disrupted or such poor-quality evidence could emerge that the chances of prosecution were slim.

One paedophile hunter claimed that he had received advice from police on gathering evidence. “I’m a bit of a nightmare, my evidence is all over the place,” he told The Independent. The man, who declined to be named, drew a distinction between what he called paedophiles – serial offenders that he told police about before he filmed them – and “nonces” whom he did not. “You can gauge what a person is like, we can read them,” he said.

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In an interview with Radio Five Live earlier this year, Scumm Buster said that the group would cease operations if someone was attacked as a result of what they were doing in exposing the identities of potential paedophiles.

“We’re vigilantes definitely,” he said. “We are not there to hurt anybody but we are there to get an explanation…. We will never hurt a single person.

“I would like to warn paedophiles we are coming for you and we will do our best to catch you.”

Other “paedophile hunters” dissociated themselves with Letzgo Hunting, which has declined to reveal their identities or details other than that they are all parents, and that the founder has a background in “security”.

None of their claimed arrests has so far resulted in a prosecution, but the activity of another group has resulted in a guilty plea. Maurice Ingram, 66, pleaded guilty to attempted sexual grooming in July after he was met by a vigilante called Stinson Hunter, instead of the teenage girl he expected.

Darren Martin, an IT expert from Church Gresley, Derbyshire, was charged this week with attempted grooming over another sting by Mr Hunter who posted the confrontation online. Police considered whether Mr Hunter, who says he inspired Letzgo Hunting, could be charged with any offence, but prosecutors said there was no realistic prospect of conviction.

A spokesman for the Association of Chief Police Officers said: “Those who take this approach to exposing paedophiles could be breaking the law and may find themselves at the centre of an investigation or prosecution.”

The groups have similar methods, and seek public support for what they are doing. One, Daemon Hunter, advertises for area co-ordinators and “paedophile baiters”.

In an apparent sideswipe at Letzgo Hunting, Mr Hunter – who works with three other men and said he had been doing it on and off for three-years – said in a statement that he was considering stopping his actions because of the “irresponsible actions of other groups”.

He described the current situation as a “complete shambles” and added: “All we ever wanted was to change the way the police work, make parents be more vigilant… now it seems to be getting lost in suicides… and blurred-out videos,” he said.