Facebook's proposal to move to an end-to-end encryption privacy model "poses an existential threat to child protection", a National Crime Agency (NCA) official has warned.
Rob Jones, director of threat leadership at the agency, said the move by the social media giant appears to put profits ahead of user safety.
His comments were made at a virtual press conference as one of Britain's most prolific paedophiles David Wilson was sentenced for 96 child sex abuse offences.
Wilson has been jailed for 25 years after he used fake social media profiles to pose as girls and get young boys to send him indecent images - he approached up to 5,000 boys online, according to the NCA.
The agency said Wilson would not have been brought to justice without evidence from Facebook.
Mr Jones said that last year Facebook sent 12 million CyberTips to the US National Centre for Missing and Exploited Children - which receives industry referrals before disseminating them to law enforcement agencies to investigate.
He said Facebook has "invoked tooling on their network which detects these images" and added it was "great" that they then referred them to law enforcement.
But Mr Jones said that end-to-end encryption, the privacy model that Facebook is set to introduce, “effectively locks them out of their own network and locks them out of their own product and the material that’s on that network”.
“What it creates is a private space where people like Wilson can masquerade as children, engage with children, groom them and potentially develop either coercive control of that individual and get them to abuse themselves and send images to them, or to meet them in the real world and abuse them directly themselves,” he said.
“We see the changes that are being invoked as a real threat to the intelligence leads that drive the UK response.”
Mr Jones said that in 2020 the NCA arrested around 4,500 offenders and 6,000 children were safeguarded, and that an “awful lot of that intelligence is driven from the CyberTip regime”.
“Invoking end-to-end encryption, which means effectively the platform can’t see its own material, threatens that regime,” he said.
Mr Jones said the NCA is asking to “maintain a position where Facebook can access their own material and report unlawful abuse of children online to the NCA and to international law enforcement”.
He said the move to end-to-end encryption “poses an existential threat to child protection and the online threat starts to get even worse at a time when we need to mitigate it and degrade it as children are more reliant upon (the internet)”.
Mr Jones said that Facebook’s “balance between (its) business objectives and public protection is wrong”.
“They appear to be putting profit, and the pursuit of profit, above the safety of the people on their platform, particularly children,” he said.
There is a “very real risk” that more offenders could move to Facebook if end-to-end encryption is installed, Mr Jones added.
“Offenders will honeypot and coalesce around where they think they are safe,” he said.
A Facebook company spokesperson said: “Child exploitation and grooming have no place on our platforms.
“Facebook has led the industry in developing new ways to prevent, detect, and respond to abuse and we will continue to work with law enforcement to combat criminal activity.
“End-to-end encryption is already the leading technology used by many services to keep people safe online and, when we roll it out on our other messaging services, we will build on our strong anti-abuse capabilities at WhatsApp.
“For example, through a combination of advanced technology and user reports, WhatsApp bans around 250,000 accounts each month suspected of sharing child exploitative imagery.”
Andy Burrows, NSPCC head of child safety online policy, said: “Wilson’s prolonged campaign of sexual abuse was exposed following a large-scale investigation by the NCA.
“If it wasn’t for the evidence provided by Facebook this would not have been possible and many more children could have been exploited.
“Despite this case highlighting the importance of tech companies being able to detect and disrupt abuse on their sites, Facebook still wants to proceed with end-to-end encryption which could prevent its moderators from uncovering prolific abuse.
“This is why the government must bring forward a comprehensive Online Safety Bill that ensures platforms face consequences if they press ahead with poor design choices that put children risk of entirely avoidable harm.”