On 4 March 2018 , Sergei Skripal , a former Russian military officer , and his daughter Yulia Skripal were poisoned in a restaurant in Salisbury . Within days of the attack , political pressure began to mount on May and her government to take action against the perpetrators , and most politicians believed that the Russian government was behind the attack . Several days later May said the agent had been identified as one of the Novichok family of agents , believed to have been developed in the 1980s by the Soviet Union . She said Britain was to push for the EU to agree new sanctions against Russia , and spoke in the House of Commons on 12 March : May said that the British government requested that Russia explain which of these two possibilities it was by the end of 13 March 2018 . She also said : " The extra-judicial killing of terrorists and dissidents outside Russia were given legal sanction by the Russian Parliament in 2006 . And of course Russia used radiological substances in its barbaric assault on Mr Litvinenko . " She said that the UK government would " consider in detail the response from the Russian State " and in the event that there was no credible response , the government would " conclude that this action amounts to an unlawful use of force by the Russian State against the United Kingdom " and measures would follow . 62 British media billed the statement as " Theresa May 's ultimatum to Putin . " 4 122 On 13 March , Home Secretary Amber Rudd ordered an inquiry by the police and security services into alleged Russian state involvement in 14 previous suspicious deaths of Russian exiles and businessmen in the UK . May unveiled a series of measures on 14 March 2018 in retaliation for the poisoning attack , after the Russian government refused to meet the UK 's request for an account of the incident . One of the chief measures was the expulsion of 23 Russian diplomats which she presented as " actions to dismantle the Russian espionage network in the UK " , as the diplomats had been identified as " undeclared intelligence agents "
were poisoned
Poisoning of Sergei and Yulia Skripal
Premiership of Theresa May