Theresa May has accused Russia of meddling in elections and planting fake stories in the media in an extraordinary attack on its attempts to “weaponise information” in order to sow discord in the west.

The prime minister spoke out against “the scale and nature” of Russia’s actions during an address at the lord mayor’s banquet, saying it was “threatening the international order on which we all depend”.

Listing Russia’s attempts to undermine western institutions in recent years, she said: “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.

“The UK will do what is necessary to protect ourselves, and work with our allies to do likewise.”

Her speech is a serious escalation of the UK’s warnings about Russia as Boris Johnson, the foreign secretary, prepares to visit Moscow before the end of the year as part of a strategy of cautious engagement with Vladimir Putin’s administration.

Since Russia’s annexation of Crimea from Ukraine, May said Russia had “fomented conflict in the Donbass [eastern Ukraine], repeatedly violated the national airspace of several European countries, and mounted a sustained campaign of cyber-espionage and disruption”.

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“This has included meddling in elections, and hacking the Danish ministry of defence and the Bundestag [German parliament], among many others,” she told the audience of City of London business figures.



“It 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.”



She said the UK did not want to “return to the Cold War, or to be in a state of perpetual confrontation” but the UK would have to act to protect the interests of the UK, Europe and rest of the world if Russia continues on its current path.

A Downing Street source said May was not making the intervention in response to any specific event but rather to a growing body of evidence that Russian agencies have been attempting to interfere with western politics.

The prime minister’s strong criticism of Russia’s activities comes in contrast to comments this weekend by Donald Trump, who said on Saturday that he believed Vladimir Putin’s denials of having meddled in the American presidential elections.

Asked by reporters if he had raised the issue of Russian interference during conversations with Putin at a summit in Vietnam during a tour of Asia, Trump said: “Every time he sees me, he says, ‘I didn’t do that.’ And I believe – I really believe that when he tells me that, he means it.”

The US president appeared to contradict that stance on Sunday when he said he was “with our agencies” on the issue.



May did not say on Monday whether she was concerned with Russian intervention in any UK democratic processes, but Ben Bradshaw, a leading Labour MP, is among those to have called for a judge-led inquiry into the possibility that Moscow tried to influence the result of the Brexit referendum.

Russia has been accused of running “troll factories” that disseminate fake news and divisive posts on social media. It emerged on Monday that a Russian bot account was one of those that shared a viral image that claimed a Muslim woman ignored victims of the Westminster terror attack as she walked across the bridge.

The account that tweeted the picture, @SouthLoneStar, was identified as a Russian bot as part of a US investigation into the country’s influence on the 2016 presidential election.



The prime minister’s attack on Russia’s actions also come as MPs on the House of Commons media committee prepare to begin an inquiry into whether Moscow has tried to interfere in British politics, which is due to hear from representatives of both Twitter and Facebook.

May told the banquet that she would do everything possible to protect Europe’s security cooperation even though the UK is leaving the EU and argued that reform of Nato would maintain a vital alliance in deterring and countering hostile Russian activity.



“It is why we have stepped up our military and economic support to Ukraine,” she said. “It is why we are strengthening our cybersecurity and looking at how we tighten our financial regimes to ensure the profits of corruption cannot flow from Russia into the UK. So we will take the necessary actions to counter Russian activity.”

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May spoke about her desire to build a “global Britain” stressing recent talks on trade with Japan and India, and her commitment to “maintaining the golden era of our relationship with China” on both economic and security terms.



But the prime minister stressed that securing “the best possible Brexit deal” with the EU was critical “to underpin our shared commitment to open economies and free societies in the face of those who seek to undermine them. Chief among those ... is Russia”.



The prime minister said she still hoped that Russia would become a strong state that plays by the rules and promotes international security as a permanent member of the United Nations security council.

“Russia can, and I hope one day will, choose this different path,” she said. “But for as long as Russia does not, we will act together to protect our interests and the international order on which they depend.”

May previously spoke out against Russia’s aggression towards eastern Europe during a visit to Estonia in September but this is her most strident language accusing Moscow of manufacturing fake stories and propaganda.

Her former defence secretary, Michael Fallon, was also regarded as very hawkish in his approach to Russia, warning last month that Moscow’s spending on defence was twice that of the UK.



Since resigning at the beginning of this month over inappropriate conduct towards women, he has been replaced by Gavin Williamson, the former chief whip.



May also used her lord mayor’s speech to condemn the Myanmar regime over the treatment of the Rohingya Muslim minority, more than 600,000 of whom have fled the country’s north-western Rakhine state for neighbouring Bangladesh.

She said: “This is a major humanitarian crisis which looks like ethnic cleansing. And it is something for which the Burmese authorities – and especially the military – must take full responsibility.”