Russia used trolls and bots to unleash disinformation on to social media in the wake of the Salisbury poisoning, according to fresh Whitehall analysis. Government sources said experts had uncovered an increase of up to 4,000% in the spread of propaganda from Russia-based accounts since the attack,– many of which were identifiable as automated bots.

Theresa May highlighted the cyber-threat from Russia in her Mansion House speech earlier this year, telling the Kremlin: “I have a very simple message for Russia. We know what you are doing. And you will not succeed.”

Twitter diplomacy: how Russian embassy trolls UK government Read more

But civil servants identified a sharp increase in the flow of fake news after the Salisbury poisoning, which continued in the runup to the airstrikes on Syria.

One account, @Ian56789, was sending 100 posts a day during a 12-day period from 7 April, and reached 23 million users, before the account was suspended. It focused on claims that the chemical weapons attack on Douma had been falsified, using the hashtag #falseflag. Another account, @Partisangirl, reached 61 million users with 2,300 posts over the same 12-day period.

Experts say that accounts can be amplified by automated means.

The prime minister discussed the matter at a security briefing with fellow Commonwealth leaders Malcolm Turnbull, Jacinda Ardern and Justin Trudeau earlier this week. They were briefed by experts from GCHQ and the National Cyber Security Centre about the security situation in the aftermath of the Syrian airstrikes.

May said afterwards: “Russia is using cyber as part of a wider effort to undermine the international system. This disinformation campaign is 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. We must do all we can at every turn to challenge this.”

The prime minister claimed that this particular fake-news campaign had failed, because she had managed to convince Britain’s EU allies, the G7 and Nato that there was “no other plausible explanation than Russia is to blame” for the nerve-agent attack on former spy Sergei Skripal and his daughter Yulia.

Labour leader Jeremy Corbyn has called for “a shift from the rhetoric of endless confrontation with Russia”, believing that it “could also help lower the temperature and make a UN consensus for multilateral action to end Syria’s agony more likely”.

• This article was amended on 27 April 2018 to replace the word “bot” with “account” in relation to @Ian56789 and @Partisangirl.

