Children in the UK could be at risk of sexual threat from up to 850,000 offenders, the National Crime Agency has estimated.
They have estimated the number ranges between 550,000 and 850,000.
The newly published research has inflated the number considerably, with previous estimates setting the minimum of 300,000 offenders.
Previous figures were calculated by considering the number of registered sex offenders and those using sites on the dark web to look at images of child abuse.
In its annual National Strategic Assessment, the NCA said plans to introduce end-to-end encryption for Facebook messages may hamper its ability to catch paedophiles.
‘Offenders will go undetected’
The agency had previously had success in catching prolific serial offenders, using social media.
In one case, prolific offender David Wilson, a labourer from King’s Lynn, Norfolk, used fake identities on social media to pose as teenage girls and groom and blackmail boys to send him abuse images.
Information from Facebook and thousands of messages were key to his successful prosecution for 96 sexual offences against 51 boys aged four to 14, for which he was jailed for 25 years.
The NCA assessment said: “Information from Facebook and evidential material containing over 250,000 messages was crucial to Wilson facing justice.
“However, plans for end-to-end encryption will prevent access to message content and likely mean other offenders like Wilson will go undetected.
Andy Burrows, Head of Child Safety Online Policy at the NSPCC, called on the Secretary of State for Digital, Culture, Media and Sport - Oliver Dowden - to take action.
‘700,000 likely pose a threat’
Burrows said: “This assessment underlines that the scale and complexity of child abuse has never been greater, with 700,000 adults across the UK likely to pose a sexual threat to children.
“This is an urgent challenge and it’s clear we can’t continue with the status quo, where it’s left to law enforcement to investigate child abuse but social networks fail to do enough to proactively prevent and disrupt it from happening in the first place.
“It couldn’t be clearer that Oliver Dowden needs to deliver a more ambitious Online Safety Bill, with success being judged on whether it does everything necessary to prevent inherently avoidable online abuse.”
Child abuse is only one form of crime which has risen during lockdown, according to the NCA.
At the beginning of the first Covid lockdown last March, the NCA began targeting high-harm child sex offenders, and by the end of the year had identified more than 1,000 suspects, had along with police arrested 320 people, and safeguarded more than 400 children.
Of the 320 arrested, 122 were targeted by the NCA, and included 17 people in positions of trust, including the deputy head of a primary school who was later jailed.
‘We must move to a place of zero tolerance’
NCA director general Lynne Owens called on social media companies to shut down all avenues for criminals to use their platforms.
She said: “While the NCA will continue to lead the fight to cut serious and organised crime, it is imperative that technology and social media companies match this intensity, building in safety by design and closing down all avenues for offenders to exploit their platforms.
“In particular, we must move to a place of zero tolerance for the presence of such material online in order to raise the bar to offending and, most importantly, protect children.”
Other forms of crime thought to be rising are bribery and corruption, cyber crime, drug dealing, fraud and money laundering.
A Facebook spokesman said: “Child exploitation has no place on our platforms and Facebook will continue to lead the industry in developing new ways to prevent, detect and respond to abuse.
“End-to-end encryption is already the leading security technology used by many services to keep people safe from hackers and criminals.
“Its full rollout on our messaging services is a long-term project and we are building strong safety measures into our plans.”
Full encryption will be brought in during 2022 and the company said it is already focusing on stopping abuse in other ways, including using AI to detect harmful behaviour, safety notices in Messenger and a feature to stop adults messaging under-18s.