Theresa May launched a stunning attack on Russia on Monday evening, accusing the Kremlin of meddling in elections and carrying out cyber espionage.
The Prime Minister said Vladimir Putin's government was trying to 'undermine free societies' by 'planting fake stories' to 'sow discord in the West,' she said in a major foreign policy speech at Lord Mayor's Banquet at Mansion House.
In comments that marked a stark contrast to US President Trump who said he believed Putin's denial of interfering in the election, May said she had a 'very simple message', warning the Russian President he must chose a 'different path'.
They also contrasted with her own Foreign Secretary Boris Johnson who told the foreign affairs select committee last week he had seen no evidence of Russian meddling in elections.
'The UK will remain unconditionally committed to maintaining Europe's security,' May said in the speech on Monday night.
'The comprehensive new economic partnership we seek will underpin our shared commitment to open economies and free societies in the face of those who seek to undermine them.'
The British government is playing one of its strongest cards in the Brexit negotiations by offering to put its defence and security assets at the disposal of the EU in the hope of winning concessions on future trading and economic relations.
The country has bigger defence budgets than any other EU member state and its diplomatic and intelligence services are among the most extensive in Europe.
The government also argues it is one of the leading EU contributors to a range of security measures, such as data and evidence sharing, extradition measures and to the EU's police agency Europol.
May on Monday accused Russia of fomenting violence in eastern Ukraine, of repeatedly violating the national airspace of several European countries, and mounting a campaign of cyber attacks.
She also accused Russia of meddling in elections and hacking the Danish defence ministry, the German parliament and its state-media of planting fake stories and photo-shopped images in an attempt to undermine western institutions.
May said the government is working to reform NATO so it is better placed to counter Russian hostility and has stepped up military and economic support to Ukraine.
'We will take the necessary actions to counter Russian activity,' she said.
May also said she wanted better relations with Russia if it worked to promote peace.
'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.'
Additional reporting by Reuters.