Ofcom has launched investigations into the compliance of four companies – which collectively run 34 pornography sites – with new age-check requirements under the UK’s Online Safety Act, the regulator said.

The regulator will examine whether websites run by 8579 LLC, AVS Group Ltd, Kick Online Entertainment S.A. and Trendio Ltd have done enough to protect children from watching inappropriate content.

Together, the websites run by the companies are visited by nine million people in the UK each month, the regulator said.

They join other companies under investigation by Ofcom including 4chan, which has also been accused of allowing users to access illegal content.

The new Online Safety Act allows Ofcom to impose fines of up to £18 million or 10 per cent of worldwide revenue, whichever is larger. It can also get a court order for “business disruption measures”, which can include forcing payments providers or advertisers to stop providing services, or banning internet companies from allowing customers to access a given website.

First, Ofcom will investigate the companies to check whether their websites have the requisite checks. If failures are found, it will issue them with notices that can they appeal before a final decision is made.