Russian-controlled “bot” accounts have bombarded social media with anti-Western propaganda 45,000 times since the chemical attack in Syria as part of a “dirty disinformation war” by the Kremlin.

Whitehall officials have measured a 4,000 per cent increase in posts from automated Twitter and other website accounts linked to Moscow in the past two weeks.

Some accounts, which are disguised as Western in origin to make them appear legitimate, pumped out up to 200 posts per day.

Theresa May said Russia was using its cyber capabilities “as part of a wider effort to undermine the international system”.

The Prime Minister said the disinformation campaign was “not just aimed at social media and the UK – it is intended to undermine the actual institutions and processes of the rules based system, such as the Organisation for the Prevention of Chemical Weapons”.