Concern about Russian influence in British politics has intensified as it emerged that more than 400 fake Twitter accounts believed to be run from St Petersburg posted almost 45,000 messages about Brexit in the 48 hours around ahead of last year's referendum in an attempt to sow discord during the vote on whether to leave the European Union.
Researchers at the University of Edinburgh identified 419 accounts operating from the Russian Internet Research Agency (IRA) attempting to influence UK politics out of 2,752 accounts suspended by Twitter in the US, according to The Guardian.
Meanwhile The Times cited research from an upcoming paper by data scientists at Swansea University and the University of California, Berkeley, which it said showed accounts based in Russia had tweeted about Brexit in the days leading up to the June 23 vote.
The Times said most of the tweets seen by the newspaper encouraged people to vote for Brexit, although a number advocated remaining in the EU. It quoted Tho Pham, one of the paper's authors, as saying ''the main conclusion is that bots were used on purpose and had influence''.
The research tracked 156,252 Russian accounts that mentioned #Brexit, including one, Svetal1972 which posted 92 tweets between 20 and 24 June, including one calling for Britain to ''make June the 23rd our Independence Day''.
It said many of the messages appear to have come from automated accounts known as bots or from cyborg accounts which are heavily automated but have some human involvement.
In the 23 June 2016 referendum, 17.4 million votes, or 51.9 per cent of votes cast, backed leaving the EU while 16.1 million votes, or 48.1 per cent of votes cast, backed staying.
Russia has repeatedly denied meddling in Brexit. Russian officials say the West is whipping up anti-Russian hysteria around Moscow's alleged involvement in both the US presidential election and Brexit.
In Britain, a parliamentary committee has written to Facebook's Mark Zuckerberg asking for information on any paid-for activity by Russian-linked Facebook accounts around the EU referendum and the 2017 national election.
British Prime Minister Theresa May on Monday accused Russia of meddling in elections and said the government would maintain its commitment to protecting Europe after Brexit.
''We will take the necessary actions to counter Russian activity,'' she said.
Damian Collins, the chairman of the Commons culture, media and sport select committee, which is investigating fake news, said the Russian agency appeared to be attempting to divide society and destabilise politics.
The Conservative MP wants Twitter to tell the committee how it believes Russia has been attempting to influence UK politics.
''What is at stake is whether Russia has constructed an architecture which means they have thousands of accounts with which they can bombard [us] with fake news and hyper-partisan content,'' he said.
''We need to understand how widespread it is and what the impact is on the democratic process.''
Collins has demanded that Twitter's chief executive, Jack Dorsey, supply examples of posts from the Internet Research Agency about British politics – citing concern at possible ''interference by foreign actors in the democratic process'' of the UK.
''This is information they hold and I can't see any reason they should be delaying supplying it,'' he said.
Prof Laura Cram, director of neuropolitics research at the University of Edinburgh, told The Guardian that at least 419 accounts tweeted about Brexit a total of 3,468 times – mostly after the referendum had taken place.
Archives of the now deleted Russian accounts show they included people purporting to be a US Navy veteran, a Tennessee Republican and a Texan patriot – all tweeting in favour of Brexit.
Labour deputy leader Tom Watson urged Theresa May to ''bring political pressure to bear on tech giants to reveal the extent to which their platforms have been hijacked, and to take action against agents of the Russian state who use their platforms to disseminate misinformation and untruths''.
He said tech companies including Twitter and Facebook ''haven't done enough to identify and weed out the fake profiles and automated content that pose a direct threat to our democracy''.
On Monday, May gave a speech in which she said Russia's actions were ''threatening the international order on which we all depend''.
She accused Russia of meddling in elections and planting fake stories in the media to ''weaponise information'' and sow discord in the west.
Concerns about Russia's cyber-operations have also been raised elsewhere in Europe.
Spain's prime minister, Mariano Rajoy, claimed on Monday that half of the Twitter accounts that amplified the issue of Catalan independence were registered in Russia and 30 per cent in Venezuela.
Others have voiced concerns that Russian social media accounts also sought to influence this year's French and German elections.
A spokesperson for Twitter said the company ''recognises that the integrity of the election process itself is integral to the health of a democracy. As such, we will continue to support formal investigations by government authorities into election interference as required.''