Facebook’s plans to allow encrypted messaging across all its platforms could prevent the detection of up to 20m child abuse images every year, a senior investigating officer has claimed.

Rob Jones, the director of threat leadership at the National Crime Agency, said the social media company’s goal of rolling out end-to-end encryption will stop officers from accessing “incisive intelligence” that allows them to rescue abused children.

The warning, which will alarm privacy campaigners, came as the government continued to fight the plans of Mark Zuckerberg, the Facebook chief executive, to extend encryption.

Last month, Facebook extended the option of using end-to-end encryption for Messenger voice calls and video calls – which means that nobody else, including Facebook, can see or listen to what is sent or said.

At a briefing with journalists, Jones said police are reliant on “a very fast, dynamic law enforcement response” to online sexual abuse content that allows officers to develop suspicion, belief or probable cause.

“That content will go if the current privacy model [suggested by Facebook] lands in the way it’s been described. So all those tips are at risk – all of those tips,” he said.

“When Facebook loses the insight from not being able to see the content, [abusers’] behaviour will carry on – there is nothing to suggest it won’t – but the reporting will be of a different type.

“The reporting will tell us what we already know: that we suspect Facebook has a lot of people with a sexual interest in children on there. It won’t give a level of incisive intelligence and breaks and leads that we get now, which allows us to go and get a search warrant, get through a door and rescue a child.”

In 2020, the tech industry made more than 21m referrals globally of child sexual abuse identified on its platforms to the US National Center for Missing and Exploited Children (NCMEC). Over 20m of those reports were from Facebook, the NCA said.

The home secretary, Priti Patel, will on Wednesday step up her international campaign against encryption as she meets with her G7 counterparts over the next two days, with internet safety and security dominating the agenda.

At a meeting of ministers from G7 countries, she will also launch a fund aimed at tackling child sexual abuse online.

Innovators and tech experts will be invited to apply for government funding to show the internet technology giants how they can better design their products and not increase the risk of their platforms being a safe haven for child sexual abusers.

A Facebook spokesperson 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.”