A study carried out by 89up, a British communications and social media analytics firm, has concluded that there was a substantial amount of pro-Brexit Russian media interference during the UK’s 2016 EU referendum.

In November last year, the British Prime Minister Theresa May had accused Russia of “weaponizing information,” although May refrained from directly accusing the Kremlin government of meddling in the referendum.

The 89up’s founder and chief executive Mike Harris has no doubts that the Russian state media tried to influence British politics and the EU referendum in 2016. According to Harris, Kremlin-backed news outlets Sputnik and RT published more than 260 misleading, pro-Brexit articles that were viewed about 134 million times on Twitter. Harris said the anti-EU stories were shared so extensively on Twitter that they created greater impact compared to the official Vote Leave and Leave.eu campaigns. These two campaigns gathered only 33 million and 11 million views respectively on the microblogging site, according to 89up.

Harris also said that Facebook must be more transparent regarding who spent how much on advertising during the EU referendum campaign.

“During the period of the UK referendum we need to know who did Facebook take advertising from and they need to make a proper audit to see if any Russian state actors were promoting content that would lead British voters to either conclusion, to remain in the EU or to leave the EU,” Harris said.

Today we revealed the full and staggering scale of Russian media interference in the EU referendum. https://t.co/TkEtL7GIRT pic.twitter.com/4iV42DQKWS — 89up (@89_up) February 12, 2018

According to 89up, social media activity of both RT and Sputnik spiked on the final day of the referendum. The activity of these two channels increased immensely on Twitter, matching with the increase in the Russian bot activity on that particular day. The 89up’s report claims that many articles published by RT and Sputnik during the referendum period were extremely misleading. Their stories exaggerated the facts on the migration of European refugees, immigration to the UK, the role of CIA in creating the EU, etc.

The data for 89up’s study was sourced from the tools provided by Facebook, Twitter, and BuzzSumo, as well as from other “scraping” techniques.

Facebook has widened its investigation into possible Russian interference in the EU referendum https://t.co/XCzXudOtQZ — Sky News (@SkyNews) January 17, 2018

89up has submitted its report to the UK’s Digital, Culture, Media, and Sports Committee that is currently probing the impact of fake news on the EU referendum. Last week, the committee heard evidence from Nick Pickles, UK head of public policy at Twitter, who revealed that a single troll factory tweeted about 942 messages during the referendum vote. However, Pickles asserted that the suspicious accounts failed to win a high level of engagement from Twitter users.

According to Euronews, the committee chairman Damian Collins said social media companies must notify British voters who might have been exposed to propaganda and falsehood during the campaign.

Last week, Damian Collins and other MPs visited Washington to question Google, Facebook, and Twitter about fake news on their platforms. During the hearing, senior executives from these social media companies were asked questions about possible Russian meddling in the UK’s EU referendum.