A Canadian data firm employed by multiple Brexit campaign groups spent 2 million dollars (£1.4 million) on political adverts on Facebook targeting the EU referendum, an executive from the social media giant has told MPs.
Mike Schroepfer, Facebook's chief technical officer, said Aggregate IQ spent considerable amounts targeting the Brexit vote in 2016, but he had found no records showing Cambridge Analytica, the controversial election consultants at the centre of a data scandal, had done the same.
However, Mr Schroepfer told the parliamentary inquiry into fake news that a Facebook investigation had discovered "billing and administration connections" between the two companies.
Appearing before the Digital, Culture, Media and Sport select committee, he said: "The collaboration we saw was some billing and administration contacts between the two of them.
"We would see similar people show up between the two accounts."
Committee chairman Damian Collins has repeatedly asked Facebook founder Mark Zuckerberg to provide evidence to the inquiry but the company sent Mr Schroepfer instead.
Asked to provide further details on the individuals involved, Mr Schroepfer said he had given "extensive information" to the Electoral Commission and the Information Commissioner but was hesitant to go further in public.
The companies are investigating how Facebook data may have been misused to help political campaigns target advertising on social media and whether there was collaboration between Brexit campaign groups.
Cambridge Analytica has repeatedly denied working on the EU referendum on behalf of campaign group Leave.EU, but emails provided to the committee by a former CA employee detail numerous meetings between the two organisations and an unpaid invoice for more than £40,000.
Brexit campaign groups Vote Leave and BeLeave, as well as the DUP and Veterans for Britain, paid Aggregate IQ millions of pounds for services related to the Brexit campaign, but this is the first time precise details about how it may have been used have been revealed.
Mr Schroepfer said: "I believe we are producing more extensive information for both the Electoral Commission and the Information Commissioner.
"I think we are trying to give them all the data we have on the ads, what they spent and what they are like."
On Tuesday the committee heard from Aleksandr Kogan, an academic researcher who collected data from millions of Facebook users, including more than a million Britons, and gave it to CA, in breach of Facebook's terms of service.
Mr Schroepfer insisted the data collected by Dr Kogan was not used by AIQ, which instead used "email lists" to target British voters on Facebook on behalf of Brexit campaign groups.
Facebook is making numerous changes to its platform to emphasise "safety, transparency and control" for users and user data, said Mr Schroepfer, including a "searchable archive" of political advertising in time for the UK local elections in May 2019.
"We feel a deep responsibility to solve these problems and make sure our platform is safe," he said.