But the hearing, which was live-streamed after lobbying from MEPs, failed to deliver answers from Mr Zuckerberg. The format meant questions from the 12 parliamentarians were collated, with Mr Zuckerberg only touching on broad themes at the end.

Guy Verhofstadt, the head of the liberal group in the European Parliament, demanded Mr Zuckerberg provide written answers to MEPs in the coming days.

“You have to ask yourself how you’ll be remembered. As one of the three big internet giants together with Steve Jobs and Bill Gates who have enriched our world? Or a genius who created a digital monster that is destroying our societies and democracies?” said Mr Verhofstadt, a former Belgian prime minister.

“There are a number of questions that have been put by my colleagues that I want an answer to,” said Mr Verhofstadt at the end of the hearing.

Philippe Lamberts, the co-head of the Parliament’s Green party, complained Mr Zuckerberg had failed to answer any of his questions during the session, including on whether Facebook was willing to publish country-by-country details of its business operations and tax arrangements across the EU.

“I asked you six yes-or-no answers and I got no answers. You asked for this format for a reason,” said Mr Lamberts. “This can’t be the end of the story. We will insist on a follow-up and, if needed, additional regulation.”

Mr Zuckerberg’s acceptance of an appearance before MEPs had been considered a coup for the EU after the Facebook chief rebuffed calls to give testimony before the UK House of Commons. His only previous public testimony after the fallout of the Cambridge Analytica scandal was before the US Congress last month.

But the limited format left the president of the Parliament, its Speaker, Antonio Tajani, red-faced. He assured MEPs that Facebook would have to provide written answers “question by question in the next days”.

The Parliament’s civil liberties committee has also invited senior Facebook officials including Sheryl Sandberg, chief operating officer, to face a public grilling in Brussels next month. The EU estimates up to 2.7m European Facebook users had their data improperly shared with Cambridge Analytica.

MEPs asked tougher and more specific questions than many of their counterparts in Congress, who grilled Mr Zuckerberg for a total of 10 hours last month.

Their rhetoric was also more clearly anti-Big Tech, with Mr Verhofstadt comparing Facebook to the large technology company in the bestselling dystopian novel The Circle by Dave Eggers.

EU lawmakers also addressed head-on the question of whether Facebook was a monopoly. They sought commitments for changes such as allowing users to completely opt out of targeted advertising and called for a discussion on technical points, such as whether algorithms should be made public.

Manfred Weber, the leader of the centre-right European People’s party grouping, kicked off the questioning by following up on a question asked by California Democratic Senator Kamala Harris in the Congressional hearings. Mr Weber asked Mr Zuckerberg if he had personally made the decision not to notify users about the massive data leak to Cambridge Analytica.

Mr Zuckerberg did not answer the question and Facebook has given little information about how it decided, on discovering the leak in 2015, not to make it public.

Many of his answers were the same as those given to Congress: accepting the “right” kind of regulation, denying claims that it is a monopoly, and promising to comply with the “principles” of the General Data Protection Regulation around the world.

The hearing came three days ahead of the rollout of the EU’s landmark new privacy regulations which will give European authorities the power to fine tech giants up to 4 per cent of their annual turnover for privacy breaches. Mr Zuckerberg said Facebook expects to be fully complaint by May 25, this Friday.

Jan Philipp Albrecht, a Green MEP who led the GDPR through the European Parliament, repeatedly pushed Mr Zuckerberg on whether the social media giant would or would not share personal data of Facebook and WhatsApp users.

Claude Moraes, a UK Labour MEP and chair of the civil liberties committee, demanded Mr Zuckerberg provide MEPs with “a moral and legal commitment” that Facebook would respect the privacy of EU citizens. Neither MEP was given an answer.

Rightwing members used the opportunity to ask if Facebook’s algorithms were harming free speech by censoring anti-establishment or populist political content.

Nigel Farage, the pro-Brexit former Ukip leader, called for the creation of a “social media bill of rights” to protect free speech online.

“Since January, you’ve changed your modus operandi and that has led to a very substantial drop in [page] views for those who are right of centre,” maintained Mr Farage.

Shares in Facebook were almost flat in afternoon trading in New York, having returned to the price before the Cambridge Analytica revelations in the last couple of weeks.

Daniel Ives, chief strategy officer at GBH Insights, said Brussels had produced a “much tougher line of questioning” that seen in Washington, but he believed the stock was rebounding as fears of regulation started to fade into the background.

“While we expect more back and forth between the EU and Facebook over the coming weeks, we view today as another step forward for Zuckerberg post-Cambridge,” he said in a note.

(Published by The Financial Times, May 23, 2018)