Keir Starmer will ban under-16s from major social media apps such as TikTok, Instagram and X in sweeping restrictions described as “Australia plus”, the Guardian understands.

Teenagers will be banned from all the main social platforms and online products that are not covered by the ban – such as gaming apps – will face new restrictions such as having the option to chat to strangers removed. There will also be restrictions for older teenagers up to the age of 18 that prevent “scrolling” late at night – after 8.30pm.

Government sources said protecting teenagers from harmful addictive content, such as infinite scrolling, as well as contact with strangers were the key drivers of the hardline measures. Under-18s will also be banned from accessing romantic or sexual AI chatbots. “There are no half measures here,” a government source said.

The government may need to legislate to enforce the ban and to give itself flexibility to adapt to new technology, though the Children’s Wellbeing and Schools Act does give ministers some powers already.

In Australia, which is already enforcing a ban, under-16s are restricted from 10 major platforms – TikTok, YouTube, Instagram, Reddit, Facebook, X, Threads, Snapchat, Twitch and Kick. UK government sources indicated that the bans on major platforms would apply to a similar range of apps.

On Sunday, the government said that nine out of 10 parents backed a minimum age of 16 for accessing the apps in responses supplied to its “growing up in the online world” consultation.

Nearly 9 in 10 (88%) said fewer children would be exposed to inappropriate or harmful content. Almost two-thirds of young people who responded said restricting the high-risk features would make them safer online.

On Sunday, the culture secretary, Lisa Nandy, said restrictions on social media would not be “the silver bullet solution” but they would better protect young people.

“I don’t want to get ahead of the prime minister’s announcement. But when we launched the consultation, it was a question of how we better protect young people online, not if we do so.

“And one of the things that a social media ban does and has been shown to do in Australia is that – although it doesn’t stop all young people going online and on to social media apps – it does mean that you … stop the situation where kids as young as eight, nine, 10, 11 are going on to social media sites because all of their friends are on them at an age when, frankly, they’re not really emotionally equipped to be able to cope with it.

She added: “I don’t think banning social media on its own is the silver bullet solution, but I do think Australia has shown very clearly that it has a significant role to play.”