Paedophile hunters can continue to pose as children to catch perverts looking for sex with children online after a landmark court ruling.
An ongoing legal battle could have seen any evidence gathered by "vigilante" groups, which have soared in number across the UK, banned from the courts.
Legal teams acting for two men allegedly snared by Dark Justice, an undercover organisation whose activities have already led to 42 convictions, claimed prosecutions using evidence gathered by such groups "diminished the integrity of the court process".
Defence lawyers argued that Dark Justice should be subject to regulation, to prevent the law from being "evaded" and that any evidence gathered by them should not be used in court.
The defence teams claimed the cases against the two men, who are accused of turning up to meet who they thought were children before being confronted by Dark Justice, should be dropped due to the way the evidence against them was gathered.
If a judge ruled that evidence gathered by Dark Justice was not admissible in court on those grounds, similar cases across the country would have collapsed.
In a detailed judgement given at Newcastle Crown Court, Mr Justice Langstaff said there was no legal requirement for the activities by the group to be subjected to controls.
The judge said the defence team's argument that evidence gathered by Dark Justice should be governed by the Regulation of Investigatory Powers Act 2000 (RIPA), which public bodies are bound by, was rejected.
Justice Langstaff said Dark Justice were acting as private individuals, not public authorities, and had not been asked by the police to conduct their activities.
The judge said: "The police have neither expressly nor implicitly authorised members of Dark Justice to act as covert human intelligence Sources, nor invited them expressly or implicitly to do so.
"The members of Dark Justice have acted as private citizens throughout.
"Authorisation of them by any public authority to act as a covert human intelligence source was and is not required by law.
"The provisions of RIPA are directed towards the behaviour of public authorities rather than private citizens. There is no legal requirement for their activities to be subject to any of the controls that might have been a condition of authorisation."
Justice Langstaff said arguments around entrapment in relation such groups should be dealt with on a case to case basis.
The judge added: "There may remain an argument that in doing what they did, Dark Justice did not act in the public interest to reduce crime, but rather
acted in a manner contrary to the public interest by helping to create it where it might not otherwise have occurred."
The judge said the proceedings against the two men who brought the arguments to court would continue.
A number of similar cases which had been put on hold until the judge's decision will now continue through the court process.
Prosecutor Michael Bunch told the court: "All relevant cases were adjourned pending the judgement."
Dark Justice is an anonymous group consisting of two men who pose as children online, on adult dating sites and other social media, to snare people looking to engage with children.
The men claim to be underage children when adults contact their fake profiles and turn up with a video camera and the police en route if any meeting is arranged.
Speaking after the ruling, Dark Justice said: "We are member of the public and have never been employed by the police or any government agency.
"We do this because we are concerned citizens who worry about the future of our children.
"If we weren't proactively catching these people it would be real children, real victims.
Detective Superintendent Michael Jones said in a statement that members of Dark Justice are not encouraged in the activities they do by the police and, if anything, are discouraged and in no way considered as taking steps on behalf of or at the request of a public authority.
Detective Superintendent Michael Barton said in his statement that forces neither work with nor endorse the activities of those such as Dark Justice.
He spoke of concerns about the public safety of their activities and said the policy "is not to forge a convenient, quasi-volunteer arrangement to somehow discharge the responsibility of the police to investigate crime".