The head of a parliamentary inquiry into allegations of Russian interference in the EU referendum has said social media companies should notify British voters who may have been exposed to falsehoods and propaganda spread during the campaign.

Damian Collins, chair of the digital, culture, media and sport select committee, was speaking after he and other MPs travelled to Washington to grill the global policy leads at Google, Facebook and Twitter.

He told the Observer that he expects the companies to do in Britain what Twitter is planning to do in the US where it says it is “working to identify and inform individually” users who saw tweets during the 2016 US presidential election produced by accounts tied to the Kremlin-linked Internet Research Agency.

Twitter has said there was evidence of only a very small role played by the Internet Research Agency, a so-called troll factory in St Petersburg, and it had so far identified only 49 accounts, which tweeted 942 times and scored 461 retweets and 637 likes.

Collins also cited new research claiming that the social media reach of heavily pro-Brexit coverage by Russia Today and Sputnik – both Kremlin-backed media outlets – may have had more influence than the two main Leave campaigns.

Some of the Russian company’s most shared media articles on Brexit were found to have achieved 200m “impressions” for tweets.

This compared with 33m for Vote Leave and 11m for Leave.eu, according to 89up, a campaigns agency which has worked on lobbying initiatives for clients including Best for Britain, the campaign group fighting to keep the UK in the EU.

“I think that we will also be heavily informed by other research looking into how social media messaging from RT and Sputnik ... was shared and who shared it. It could be people who were sharing or distributing their content [that] may also have been linked to other Russian actors like the Internet Research Agency that was spreading fake news,” said Collins.

Mike Harris, CEO of 89up, said the Kremlin-backed news channels had three times greater impact on Twitter than both the official Leave campaigns combined.

“The Russian government has two media outlets based in the UK, Sputnik and Russia Today (RT), who ran hundreds of misleading news articles in the run-up to the EU referendum that were seeded across social media. We need parliament to get to grips with a clear and deliberate attempt by an autocratic foreign power to interfere in our democracy,” Harris said.

The data compiled by 89up was sourced from tools provided by Twitter, Facebook, the social marketing company BuzzSumo and other “scraping” methods.