LONDON, Dec 16 (Reuters) - Britain's online safety

regime came into force on Monday, requiring social media

companies like Meta's Facebook and ByteDance's TikTok

to take action to tackle criminal activity on their platforms

and make them safer by design.

Media regulator Ofcom said it had published its first codes

of practice on tackling illegal harms such as child sexual abuse

and assisting or encouraging suicide.

Sites and apps have until March 16, 2025, to assess the

risks illegal content poses to children and adults on their

platforms, Ofcom said.

After the deadline, they will have to start implementing

measures to mitigate those risks, such as better moderation,

easier reporting and built-in safety tests, Ofcom said.

Ofcom Chief Executive Melanie Dawes said the safety

spotlight was now firmly on tech companies.

"We'll be watching the industry closely to ensure firms

match up to the strict safety standards set for them under our

first codes and guidance, with further requirements to follow

swiftly in the first half of next year," she said.

The Online Safety Act, which became law last year, sets

tougher standards for platforms such as Facebook, YouTube and

TikTok, with an emphasis on child protection and the removal of

illegal content.

Under the new code, reporting and complaint functions will

have to be easier to find and use. High-risk providers will be

required to use automated tools called hash-matching and URL

detection to detect child sexual abuse material, Ofcom said.

The regulator will be able to issue fines of up to 18

million pounds ($22.3 million) or 10% of a company's annual

global turnover if they fail to comply.

Britain's Technology Secretary Peter Kyle said the new codes

were a "material step change in online safety".

"If platforms fail to step up the regulator has my backing

to use its full powers, including issuing fines and asking the

courts to block access to sites," he said.

(Reporting by Paul Sandle; Editing by Emelia Sithole-Matarise)