In a letter to chief executive Mark Zuckerberg, Home Secretary Priti Patel and her counterparts in the US and Australia outlined their fears that such a move could hinder law enforcement.

Although she has only been in the position for a few months, Patel has already decried the use of encryption by messaging services such as WhatsApp and Telegram at a meeting of the Five Eyes intelligence alliance.

The letter demands that end-to-end encryption, which means no-one apart from the sender and recipient can read or modify the messages, will not be introduced until assurances are made that there will be “no reduction to user safety and without including a means for lawful access to the content of communications to protect our citizens.”

Patel said: “So far nothing we have seen from Facebook reassures me that their plans for end-to-end encryption will not act as barrier to the identification and pursuit of criminals operating on their platforms.

“Companies cannot operate with impunity where lives and the safety of our children is at stake, and if Mr Zuckerberg really has a credible plan to protect Facebook’s more than two billion users it’s time he let us know what it is.”

This plea could have a broad effect on Silicon Valley companies, with impacts felt by Apple, Google and Microsoft, as well as those behind smaller encrypted chat apps like Signal.

Washington has called for more regulation and launched anti-trust investigations against many tech companies, criticising them over privacy lapses, election-related activity and dominance in online advertising.

Speaking at an event in Washington earlier this week, associate deputy attorney general Sujit Raman said the National Center for Missing and Exploited Children received more than 18 million tips of online child sex abuse last year, over 90 per cent of them from Facebook.

He estimated that up to 75 per cent of those tips would “go dark” if social media companies like Facebook were to go through with encryption plans.

While WhatsApp, which is also owned by Facebook, has been using encryption for years, the platform is less conducive to grooming as users need to have the personal phone number of the recipient to contact them. Facebook’s search function allows anyone to contact anyone else through a simple name search.

Tony Stower, the NSPCC’s head of child safety online, said that Zuckerberg’s response would be a “defining moment for him and for children”, adding: “Facebook’s encryption plans show that when it comes to tackling child abuse, they want to go back to the digital dark ages.

“It’s an absolute scandal that Facebook are actively choosing to provide offenders with a way to hide in the shadows on their platform, seamlessly able to target, groom and abuse children completely undetected.”

But Facebook said it “strongly” opposes “government attempts to build backdoors” because they would “undermine the privacy and security of people everywhere”.

Antigone Davis, Facebook’s global head of safety, told the Reuters news agency that the company was looking at ways to prevent inappropriate behaviour and stop predators from connecting with children.

This approach “offers us an opportunity to prevent harms in a way that simply going after content doesn’t,” she said.

In practice, the agreement would empower the UK government to directly request data from US tech companies, which remotely store data relevant to their own ongoing criminal investigations, rather than asking for it via US law enforcement officials.

In a letter to chief executive Mark Zuckerberg, Home Secretary Priti Patel and her counterparts in the US and Australia outlined their fears that such a move could hinder law enforcement.

Although she has only been in the position for a few months, Patel has already decried the use of encryption by messaging services such as WhatsApp and Telegram at a meeting of the Five Eyes intelligence alliance.

The letter demands that end-to-end encryption, which means no-one apart from the sender and recipient can read or modify the messages, will not be introduced until assurances are made that there will be “no reduction to user safety and without including a means for lawful access to the content of communications to protect our citizens.”

Patel said: “So far nothing we have seen from Facebook reassures me that their plans for end-to-end encryption will not act as barrier to the identification and pursuit of criminals operating on their platforms.

“Companies cannot operate with impunity where lives and the safety of our children is at stake, and if Mr Zuckerberg really has a credible plan to protect Facebook’s more than two billion users it’s time he let us know what it is.”

This plea could have a broad effect on Silicon Valley companies, with impacts felt by Apple, Google and Microsoft, as well as those behind smaller encrypted chat apps like Signal.

Washington has called for more regulation and launched anti-trust investigations against many tech companies, criticising them over privacy lapses, election-related activity and dominance in online advertising.

Speaking at an event in Washington earlier this week, associate deputy attorney general Sujit Raman said the National Center for Missing and Exploited Children received more than 18 million tips of online child sex abuse last year, over 90 per cent of them from Facebook.

He estimated that up to 75 per cent of those tips would “go dark” if social media companies like Facebook were to go through with encryption plans.

While WhatsApp, which is also owned by Facebook, has been using encryption for years, the platform is less conducive to grooming as users need to have the personal phone number of the recipient to contact them. Facebook’s search function allows anyone to contact anyone else through a simple name search.

Tony Stower, the NSPCC’s head of child safety online, said that Zuckerberg’s response would be a “defining moment for him and for children”, adding: “Facebook’s encryption plans show that when it comes to tackling child abuse, they want to go back to the digital dark ages.

“It’s an absolute scandal that Facebook are actively choosing to provide offenders with a way to hide in the shadows on their platform, seamlessly able to target, groom and abuse children completely undetected.”

But Facebook said it “strongly” opposes “government attempts to build backdoors” because they would “undermine the privacy and security of people everywhere”.

Antigone Davis, Facebook’s global head of safety, told the Reuters news agency that the company was looking at ways to prevent inappropriate behaviour and stop predators from connecting with children.

This approach “offers us an opportunity to prevent harms in a way that simply going after content doesn’t,” she said.

In practice, the agreement would empower the UK government to directly request data from US tech companies, which remotely store data relevant to their own ongoing criminal investigations, rather than asking for it via US law enforcement officials.