Online pornography depicting strangulation or incestuous relationships will be banned from early November, the government has announced.
From 6 November, it will be illegal to possess or publish porn which shows strangulation or suffocation, depicts sexual activity between people who are related or shows adults role-playing as children under 16.
The new rules follow a review into porn regulation in 2025 which found depictions of choking were "rife" on popular porn sites and had helped normalise the act among young people.
Conservative peer Baroness Gabby Bertin, who headed the review, said the news came "not a moment too soon".
She told the Press Association the change in law would "send the unequivocal signal" to companies that host and facilitate porn, and also to wider society, that "extreme and violent content that encourages real-life harm is not acceptable".
Her independent review, commissioned by former Prime Minister Rishi Sunak's government, cited an account of a 14-year-old boy asking a teacher how to choke girls during sex.
It warned that people imitating such behaviour "may face devastating consequences".
Non-fatal strangulation is already an offence if someone does not consent - but its depiction online is currently not illegal.
Amendments to the Crime and Policing Bill, which became law in April, sought to ensure such content would be captured by the legislation and made criminal offences in England and Wales.
Justice minister Alex Davies-Jones said it was not about "criminalising harmless sexual preferences".
But she said "porn can shape what people think a healthy relationship looks like, especially young people". Content which "normalises, or even glorifies" violence against women can "blur the line with what is acceptable in real life", she said.
"If you've got this material, delete it. If you're sharing it, stop," Davies-Jones added.
"It's not as harmless as you may think, and after 6 November, it is criminal."
The new offences each carry a maximum penalty of five years' imprisonment, for publication.
According to the government, this could include uploading, posting or otherwise making the content available to someone online.
Possession, meanwhile, could include keeping an image stored on a phone, computer or in cloud storage, the government says.
Someone found to be in possession of images depicting sexual activity involving a person pretending to be under 16 could face up to three years' imprisonment, after 6 November.
Those found to be in possession of images depicting strangulation, suffocation or penetrative sexual activity between certain relatives could face up to two years' imprisonment.
Porn that shows or depicts sex between step or foster-relations where one person is pretending to be under 18 will also be captured by the new offences.
Durham University law professor Clare McGlynn - who has previously warned widely available extreme content normalises sexual violence - welcomed the laws taking full effect.
"This is a potential turning point, the commencement of these laws marking a line in the sand when we decided that we were no longer going to accept the normalisation of sexually violent content in pornography," she told the BBC.
But she said questions remained over how swiftly tech platforms and regulators would act to remove and mitigate the spread of violating material.
"While these are criminal offences, this is not about prosecuting individuals, but transforming the online pornographic landscape and that requires the platforms and regulator to act," Prof McGlynn added.
Additional reporting by Chris Vallance