Facebook “is at risk of committing a criminal offence” in the UK after a Times investigation uncovered potentially illegal terrorist and child porn content on the social network, despite moderators being made aware of it.

Using a fake Facebook profile, a Times journalist was able to befriend more than 100 supporters of terrorist group Isis (Islamic State in Syria) and join groups sharing “lewd or pornographic images of children”.

The story was published on the paper’s front page today and follows days after Press Gazette launched its campaign calling on Facebook and Google to stop destroying journalism.

Facebook’s algorithms are understood to have promoted some of the content by suggesting users join groups that had published it, according to the Times.

It said Facebook removed some of the content when contacted by the paper following it investigation, but moderators said other posts did not breach the site’s “community standards”.

These included dozens of pornographic cartoons depicting child abuse, a video showing a young child being violently abused and a video showing a jihadist holding a knife and standing over a severed head.

The Times said it was told by Facebook that this last video “did not contravene its rules against graphic violence”.

Senior lawyer Julian Knowles QC, told the paper: “In my view, many of the images and videos identified by The Times are illegal.

“One video appears to depict a sexual assault on a child. That would undoubtedly breach UK indecency laws. The video showing a beheading is very likely to be a publication that encourages terrorism.

“I would argue that the actions of people employed by Facebook to keep up or remove reported posts should be regarded as the actions of Facebook as a corporate entity.

“If someone reports an illegal image to Facebook and a senior moderator signs off on keeping it up, Facebook is at risk of committing a criminal offence because the company might be regarded as assisting or encouraging its publication and distribution.”

The investigation also prompted Yvette Cooper MP, chair of the home affairs select committee, to tell the paper it was “time the government looked seriously” at a proposal in Germany to fine social media companies “if illegal and dangerous content isn’t swiftly removed”.

After being contacted by the paper, Justin Osofsky, Facebook’s vice president of global operations, said: “We are grateful to The Times for bringing this content to our attention.

“We have removed all of these images, which violate our policies and have no place on Facebook. We are sorry that this occurred. It is clear that we can do better, and we’ll continue to work hard to live up to the high standards people rightly expect of Facebook.”

Yesterday, Press Gazette reported that £1.14bn, or 94 per cent, of the £1.217bn growth in the UK advertising market last year (which grew by 17.3 per cent to £10.3bn) went to Google and Facebook.