Police fear "paedophile hunters" are sitting on evidence of child sexual abuse during the coronavirus lockdown and are worried about a surge in vigilante action as measures are lifted.
Around 90 named groups are thought to be active in the UK, carrying out more than 100 monthly undercover sting operations before restrictions were introduced at the end of March.
Assistant Chief Constable Dan Vajzovic said the "vast majority" involve "real world" action, where suspects are confronted, and the encounters often filmed and posted online.
But during the first month of the lockdown just 16 incidents were recorded, with 15 of those limited to "e-activism", where evidence gathered in chat logs is passed to police.