“I think it is completely reasonable to say that there could’ve been a different outcome in the referendum if there hadn’t been, in my view, cheating,” said Wylie, a former contractor at Cambridge Analytica who is now at the heart of the Facebook scandal.

He was giving evidence to a parliamentary committee that’s investigating allegations first reported by the Observer that information on millions of Facebook users was scooped up without their consent. Brexit campaigners have denied any wrongdoing.

According to earlier news reports, Cambridge University researcher Aleksandr Kogan created a personality-analysis app that was used by 270,000 Facebook users, who in turn gave the app permission to access data on themselves and their friends, ultimately exposing a network of 50 million people.

Wylie also contradicted comments that Cambridge Analytica Chief Executive Alexander Nix made to the committee.

‘Untrue’

“I think Nix’s comments to your committee were misleading and dishonest,” Wylie said. “It is categorically untrue that Cambridge Analytica has never used Facebook data. Facebook data and the acquisition using Aleksandr Kogan’s app was the foundational data set of the company. That’s how the algorithms were developed.”

Cambridge Analytica immediately denied the claims on Twitter. “No company would risk basing their core offering on illegal data,” it wrote. “We engaged Dr. Kogan in good faith, and deleted his company’s data once we knew we had to. We’ve already certified this to Facebook.”

Cambridge Analytica has been under pressure since the revelations that it held vast swathes of Facebook user data after obtaining it from Kogan, who had shared the data without the social network’s permission.

Kogan has previously said he was being used “as a scapegoat” in the scandal, and that he believed he was handling the data he acquired “appropriately.”

Wylie said he had passed evidence to the committee about the firm’s involvement with Canadian company Aggregate IQ Data Services, which he had previously claimed was paid hundreds of thousands of pounds by Cambridge Analytica as part of its work for a lobby group during the 2016 referendum.

Damian Collins, head of the government body questioning Wylie, said it will publish its findings from Wednesday.

Separately, Facebook said Tuesday that Chief Executive Officer Mark Zuckerberg would not appear before the same lawmakers to give evidence. Collins had invited Zuckerberg to personally answer for a “catastrophic failure of process.”

Zuckerberg last week apologized for the Facebook’s failure to protect its users. The company reinforced this message by taking out full-page ads in British and U.S. newspapers.