Detectives fear a surge in self-styled vigilantes taking action against suspected sex offenders as lockdown restrictions are eased, with around 90 groups thought to be active in the UK.
It comes more than six months after six members of the group Predator Exposure were cleared at Leeds Crown Court over charges including false imprisonment and assault, following a sting they carried out on two men in which police said they had "overstepped the mark".
Vigilante groups operate by posing as young people online, falsely going along with conversations with potential offenders, then confronting the suspects after organising to meet face to face.
Encounters are often filmed and posted online, with some even being streamed live on social media.
More than 100 undercover sting operations were carried out in the month leading up to the announcement of lockdown restrictions in March.
Only 16 such operations were recorded during the first month of lockdown, of which all but one were limited to "e-activism", where evidence gathered in chat logs is passed to police.
Detectives have previously warned of the risks of members of the public acting as vigilantes trying to catch out sex offenders, as such stings may interfere with real police investigations or potentially lead to vulnerable people being wrongly accused.
The public confrontations have also resulted in assaults and even people taking their own lives.
In June 2018, a 56-year-old man from Huddersfield was found hanged near his home following release from a short stint in prison earlier that year after he was confronted at his doorstep by vigilantes.
Assistant Chief Constable Dan Vajzovic, the National Police Chiefs' Council's lead for online child sex exploitation activist groups, said paedophile hunting groups were still very much active and were potentially sitting on around 160 cases.
"We've seen a dramatic decrease in the number of activist group incidents since lockdown.
"The online threat persists, and we are concerned that activists may be storing up incidents to act upon once lockdown measures are released.
"We believe that's dangerous for child safety and would encourage activist groups to pass any material to police at as early a stage as possible."
"Activist groups can produce some positive results but our overall assessment is they are more harmful than they are good," Mr Vajzovic added.
"If they carry out activities and pass us material we will investigate and we encourage them to pass material to us at as early a stage as possible."
Charities such as the NSPCC have meanwhile warned that children may be at increased risk from sex offenders online as they spend more time at home in the internet and away from school friends during the coronavirus pandemic.
Mr Vajzovic said police have seen a "trickle" of vigilante stings as movement restrictions have been relaxed.
But the senior officer told of his fears that children could be at risk of abuse because information has not been passed to police and that he believes there could be a surge as groups act on evidence gathered in lockdown.
He said: "Real-world activism is a real significant concern for us. This big drop off of incidents from over a hundred a month to 16 a month is, in my view, indicative of the motivations of these groups.
"That they are actually more interested in carrying out a sting and the notoriety that that brings them than they are in protecting children.
"If there are groups out there who have information about child abuse they need to notify their local police as soon as possible and not wait to carry out a sting for their own motivations."