Websites that publish pornography must now verify the age of users as a legal requirement under new online safety rules, the Government has announced.
The draft Online Safety Bill will be strengthened to require all sites which publish pornographic content put "robust checks" in place to make sure users are 18 or over, digital minister Chris Philp confirmed on Safer Internet Day.
Campaigners have long demanded the rule to protect children from graphic images and films.
Andy Burrows, head of child safety online policy at the NSPCC, said it is right that the Government has listened to calls to fix a gap in the Online Safety Bill but still said the legislation falls short.
How will the new rules work?
Sites could use secure age verification technology to confirm a user possesses a credit card and is therefore at least 18, or use a third-party service to confirm someone's age against Government data.
The Government said the onus will be on the companies and sites themselves to decide on how best to comply with the new rules.
Ofcom may recommend the use of certain age verification technology, but the government said that the measures put in place should not process or store data that is irrelevant to the purpose of checking someone's age.
Ministers said that if sites fail to act, Ofcom, as the sector's regulator, will be able to fine them up to 10% of their annual global turnover or block their site in the UK.
And bosses of such sites could be held criminally liable if they fail to co-operate with Ofcom.
"It is too easy for children to access pornography online. Parents deserve peace of mind that their children are protected online from seeing things no child should see," Mr Philp said.
"We are now strengthening the Online Safety Bill so it applies to all porn sites to ensure we achieve our aim of making the internet a safer place for children."
Prior to this announcement, only commercial porn sites that allow user-generated content were in the scope of the Bill.
The update means all commercial porn sites are now within the scope of the proposed new rules.
Andy Burrows, head of child safety online policy at the NSPCC, said: "It's right the Government has listened to calls to fix one of the gaps in the Online Safety Bill and protect children from pornography wherever it's hosted.
"Crucially, they have also acted on our concerns and closed the 'Only Fans loophole' that would have let some of the riskiest sites off the hook despite allowing children access to extremely damaging material.
"But the legislation still falls short of giving children comprehensive protection from preventable abuse and harmful content and needs significant strengthening to match the Government's rhetoric and focus minds at the very top of tech companies on child safety."
Alex Davies-Jones, Labour's shadow minister for tech, gambling and the digital economy, said: "Labour has long called on the Government to offer security for young people online, and we're glad it has accepted our call for all pornography sites to stop children accessing them by using age-verification technology.
"We need strict age protection rules, while tightly regulating age-verification tech to ensure they are not being used to collect unnecessary personal data and to protect people's privacy online.
"Ultimately the Tories' persistent delays on online safety legislation means that another generation have grown up with access to harmful content online - they can and must do better."
