The event is part of an unprecedented international inquiry into disinformation and fake news.

Richard Allan, Facebook's vice-president of policy solutions, appeared in Mr Zuckerberg's place.

He said he took responsibility for deciding who appeared at which committee.

The session was attended by parliamentarians from Argentina, Belgium, Brazil, Canada, France, Ireland, Latvia, and Singapore as well as members of the UK's Digital, Culture, Media and Sport Committee.

Its chairman Damian Collins, has repeatedly asked Mr Zuckerberg to attend hearings.

Lord Allan, who is also a Liberal Democrat peer, faced a grilling on various Facebook policies and actions in addition to the subject of why his boss wasn't there.

It had been thought that a cache of Facebook documents, seized by MPs from a US businessman on the grounds that they were relevant to the inquiry, might be shared - but Mr Collins said that they would not be published today.

He later said that they will be published - possibly in the next week.

Lord Allan said he believed it would be unfair to take "internal conversations" and "robust comments" as the company's official position.

The Observer, which first reported the story about the documents being seized, said they included data about Facebook's privacy controls.

They had been sealed by a US court, and Facebook has demanded their return.

However, the contents of one email from 2014 were alluded to, in which a Facebook engineer reported unusual levels of Russian activity - namely that huge amounts of data were being pulled daily from devices with Russian IP addresses.

Lord Allan was asked whether any action was taken, or authorities notified.

He said the information he had was "partial at best" and that he would have to come back with more details.

He was also unable to name a single occasion on which Facebook had banned an app for breaking its rules, despite saying that it was Facebook's policy to do so.

Later on, UK Information Commissioner Elizabeth Denham told the hearing that Facebook informed her it had banned 200 apps during the summer of 2018.

"I'm not aware of any case before the revelation [of the Cambridge Analytica data scandal]", she said.

Lord Allan also acknowledged that Facebook had "damaged public trust" through some of its actions and said the firm was in favour of a "regulatory framework" for the social media giant.