LONDON, May 8 (Reuters) - Social media platforms like

Facebook, Instagram and TikTok will have to "tame" their

algorithms to filter out or downgrade harmful material to help

protect children under proposed British measures published on

Wednesday.

The plan by regulator Ofcom is one of more than 40 practical

steps tech companies will need to implement under Britain's

Online Safety Act, which became law in October.

The platforms must also have robust age checks to prevent

children seeing harmful content linked to suicide, self-harm and

pornography, the regulator said.

Ofcom Chief Executive Melanie Dawes said children's

experiences online had been blighted by harmful content they

couldn't avoid or control.

"In line with new online safety laws, our proposed Codes

firmly place the responsibility for keeping children safer on

tech firms," she said.

"They will need to tame aggressive algorithms that push

harmful content to children in their personalised feeds and

introduce age-checks so children get an experience that's right

for their age."

Social media companies use complex algorithms to prioritise

content and keep users engaged. However, the fact that they

amplify similar content can lead to children being influenced by

increasing amounts of harmful material.

Technology Secretary Michelle Donelan said introducing the

kind of age checks that young people experienced in the real

world and addressing algorithms would bring about a fundamental

change in how children in Britain experienced the online world.

"To platforms, my message is engage with us and prepare,"

she said. "Do not wait for enforcement and hefty fines - step up

to meet your responsibilities and act now."

Ofcom said it expected to publish its final Children's

Safety Codes of Practice within a year, following a consultation

period that ends on July 17.

Once it is approved by parliament, the regulator said it

would start enforcement that will be backed by action including

fines for non-compliance.