New data is the "most significant evidence yet" that Russia-backed social media accounts meddled in the Brexit referendum.

Over 150,000 Twitter accounts based in Russia tweeted about Brexit during the referendum campaign, an investigation has found.

Theresa May told Russian President Vladimir Putin that Britain "knows" what Russia is doing.

LONDON — Twitter accounts based in Russia posted 45,000 tweets about Brexit within the space of 48 hours during last year's referendum on EU membership, an investigation commissioned by The Times has found.

Data scientists at the University of Swansea and University of California, Berkeley found that over 150,000 accounts based in Russia posted content relating to Brexit in the days leading up to voting day on June 23, 2016.

These accounts had previously focused on issues like Russia's annexation of Crimea, before focusing their attention on the Brexit referendum, with the majority of tweets seen by the Times encouraging people to vote Leave.

A "massive number of Russian-related tweets was created a few days before the voting day, reached its peak during the voting and the result and then dropped immediately afterwards," the paper to be released by researchers says.

"The main conclusion is that bots were used on purpose and had influence," Tho Pam, one of the paper's main authors, adds.

The Russian accounts were most active on the day of the referendum (Thursday, June 23) and following day (Friday, June 24) when the final result became clear. The accounts posted over 39,000 tweets on Friday, June 24.

Conservative MP Damian Collins, who chairs the digital, culture, media and sport select committee, said the research is "the most significant evidence yet of interference by Russia-backed social media accounts around the Brexit referendum."

He added: "The content published and promoted by these accounts is clearly designed to increase tensions throughout the country and undermine our democratic process. I fear that this may well be just the tip of the iceberg."

Researchers at the University of Edinburgh have identified 419 accounts operating from the Russian Internet Agency attempting to influence British politics, the Guardian reports.

A Kremlin-linked account tweeted a bogus picture showing a Muslim woman ignoring victims of the Westminster bridge terrorist attack earlier this year. This picture was subsequently reported by The Sun and Mail Online.

Prime Minister Theresa May on Sunday used a speech to accuse Russia of using fake news to "sow discord" in the west and "meddle" in democratic processes.

"[Russia] is seeking to weaponise information. Deploying its state-run media organisations to plant fake stories and photo-shopped images in an attempt to sow discord in the West and undermine our institutions," May said.

"So I have a very simple message for Russia. We know what you are doing. And you will not succeed. Because you underestimate the resilience of our democracies, the enduring attraction of free and open societies, and the commitment of Western nations to the alliances that bind us."

MPs including Labour's Chris Bryant and Ben Bradshaw have repeatedly urged the UK government to up its investigation into the level of Russian interference in the EU referendum.

A spokesperson for Theresa May told Business Insider on Tuesday that the while the UK government had seen "no evidence of successful direct interference in UK democratic processes," they were taking "all the necessary steps to make sure we have the right protections in place and that our democratic processes aren't interfered with."

Hack attack

Drax Power Station, Selby, North Yorkshire, England Deborah Benbrook / Shutterstock National Cyber Security Centre chief Ciaran Martin will today confirm that Russia hacked Britain's energy grid and its agents have tried to penetrate British telecommunications services, such as BT.

It is believed Russian hackers successfully hijacked Britain's energy network this summer and intended to leave dormant in there which will disrupt the network at a later date.

Martin is expected to say: "I can’t get into precise details of intelligence matters.

"But I can confirm that Russian interference, seen by the National Cyber Security Centre over the past year, has included attacks on the UK media, telecommunication and energy sectors."