The Online Safety Act is being implemented in phases, and is intended to prevent past practices which Ofcom described as online platforms being "unregulated, unaccountable and often unwilling to prioritise people's safety over profits".

Tougher age checks for porn websites were introduced in July, though some people have pointed out these could be easily avoided with a virtual private network (VPN), which reroutes internet traffic.

In October, Pornhub's parent company told BBC News it had seen a 77% drop in UK visitors since the age checks had come in.

Baroness Beeban Kidron, founder of 5Rights Foundation, told the Today programme the fines were "nothing" to tech firms.

"Business disruption is everything," she said.

"Unless we're prepared to use the law, they're not really doing what Parliament asked them to do.

"We need a whole different attitude about the level of intensity and robustness from the regulator to say - we've got the law and we're using it."

The BBC has contacted a company called TubeCorporate, the adult content publishing platform behind AVS group Ltd sites, for a response.

The address which the firm uses is in the central American country Belize, and appears to be the registered address of a large number of companies: although they do not have physical offices there.

Also introduced this year were tougher guidelines on ensuring the internet was safer for women and girls, with Ofcom vowing to name and shame platforms that did not comply.

Critics say the Act needs to be toughened to make the internet safer, particularly for women and girls.