Evidence given by a former Facebook operations manager points to breaches in electoral law, according to Labour MP Jo Stevens.
A UK parliamentary committee believes the use of voters' Facebook data during the Brexit campaign violated electoral law, an MP told Euronews.
Labour MP Jo Stevens, who sits on the committee investigating fake news, said evidence was given on Wednesday by a former Facebook operations manager, "which if it is correct would mean that there have been breaches of electoral law in the UK both in relation to the 2016 referendum and the general election last year, we believe."
But how was the data collected and used?
"That could be done either by using data about what they liked on Facebook [or] what they'd posted on Facebook, so they could search against keywords. They could search against, for example, immigration or Brexit or something like that and create lists of thousands, tens of thousands, millions of people that could then be micro-targetted with political advertising," Stevens said.
The comments came amid mounting pressure on Facebook by British lawmakers following reports that UK-based firm Cambridge Analytica improperly obtained the personal information of more than 50 million of its users.
Cambridge Analytica was hired for Donald Trump's 2016 US presidential election campaign, and is also under scrutiny over alleged links to the Leave campaign in the UK referendum.
The British firm and leaders of Leave.EU have previously boasted about working together during the Brexit campaign. However, they have since retracted their claims, saying no contract was signed and no work was completed.
Facebook CEO Mark Zuckerberg has been summoned to appear before the committee to answer questions over the scandal.