Regulator Ofcom is set to be given the power to make tech firms responsible for protecting people from harmful content such as violence, terrorism, cyber-bullying and child abuse, the government will confirm on Wednesday.
Platforms will need to ensure that illegal content is removed quickly.
They will also be expected to "minimise the risks" of it appearing at all.
However it is not yet known what penalties Ofcom will be able to impose on those firms who fail to comply.
"There are many platforms who ideally would not have wanted regulation, but I think that's changing," said Digital Secretary Baroness Nicky Morgan.
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