Facebook's plans to roll out encryption across its messaging services could jeopardise ongoing work to combat child abuse, the Home Secretary is to warn.

Such encryption means only the sender and recipient can read messages.

"We cannot allow a situation where law enforcement's ability to tackle abhorrent criminal acts and protect victims is severely hampered," Priti Patel will tell a charity-hosted event.

Facebook says its plans for wider encryption protects users' privacy.

The National Society for the Prevention of Cruelty to Children (NSPCC), which invited Ms Patel to speak, has claimed that private messaging "is the frontline of child sexual abuse".

Encrypting messages by default could lead to the easier spread of child abuse imagery or online grooming, it has said.

In her speech, the Home Secretary is expected to demand that Facebook does more to take into account public safety when it makes changes to its platform - and in particular seriously consider the effect on children.

She will say: "Sadly, at a time when we need to be taking more action, Facebook are pursuing end-to-end encryption plans that place the good work and progress achieved so far [on fighting the issue of child abuse] in jeopardy.

"The offending will continue, the images of children being abused will proliferate - but the company intends to blind itself to this problem through end-to-end encryption which prevents all access to messaging content."

"This is not acceptable."

Facebook, however, said that "end-to-end encryption is already the leading security technology used by many services to keep people safe from hackers and criminals". Safety features are already a part of its plans, it added.

'Scrambled' messages

The minister will tell a group of international experts in child protection and law enforcement that Facebook must "take the safety of children as seriously as they do the business of selling advertising, phones and online games".

End-to-end encryption guarantees privacy by making sure only the sender or recipient can read the messages.

While it travels, it is scrambled to be unreadable, including by law enforcement. The only way to read the message is usually to get physical access to an unlocked device receiving it.

Currently, only one of Facebook's major messaging platforms - WhatsApp - uses end-to-end encryption by default. The company has plans to make the privacy feature the norm on Facebook Messenger and Instagram - but has not yet done so.

When messaging platforms are not end-to-end encrypted, tech giants such as Facebook can use automatic scanning of their users' posts to identify the sharing of known child abuse images and detect questionable use of private messaging - such as an older person chatting to underage users they do not already know.