The House of Lords has backed a ban on under-16s using social media.
Peers passed an amendment to the government's Children's Wellbeing and Schools Bill, which is currently making its way through parliament.
Lords debate as it happened - politics latest
The amendment says within 12 months of the act passing, social media sites must be required to use "highly effective" age checks to make sure no under-16s can become users.
With peers having backed the ban, the government will have the chance to overturn it in the Commons - but that's looking increasingly tricky.
The prime minister was initially opposed to such an outright ban, but pressure from opposition parties and his own backbenchers has softened his government's position.
One Labour MP told Sky's political reporter Faye Brown there was "no way" the government could whip the Parliamentary Labour Party against it, which could trigger another welfare-style rebellion.
Earlier this week, the government announced it was consulting on a ban for under-16s, with the block imposed by Australia potentially acting as inspiration.
Since that ban came into force in December, it has felt like the UK government has been moving to a similar policy.
But waiting for the three-month consultation to conclude may not be an option after Wednesday night's vote.
Peer after peer - and parent after parent - spoke of the risks and harms they felt were implicit in children using social media.
Some shared tips on how they limit their children's usage, others cited studies regarding the health impact.
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All eyes were on the Lords following campaigning from bereaved parents, celebrities, and charities - and now the bill heads back to the Commons where MPs will consider if they agree with the amendment.
It will be a test of parliamentary management for the prime minister - who has already been portrayed as weak to his backbenchers following that welfare rebellion - if he takes them on and loses.
But it seems almost certain a ban will be coming in some shape or form.
A government spokesperson said: "We will take action to give children a healthier relationship with mobile phones and social media.
"It is important we get this right, which is why we have launched a consultation and will work with experts, parents and young people to ensure we take the best approach, based on evidence."
(c) Sky News 2026: Logging off: Kids' social media ban now feels almost certain
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