WINTERSLOW

that this Government, that this country, stands up very clearly and not only calls out actions by Russia but also ensures that we have a robust response to them.”

She added that given “Russia’s record of conducting state-sponsored assassinations, and our assessment that Russia views some defectors as legitimate targets for assassinations, the Government has concluded that it is highly likely that Russia was responsible for the act against Sergei and Yulia Skripal”.

Mrs May said the only possible explanations were that “this was a direct act by the Russian state against our country, or the Russian government lost control of this potentially catastrophically damaging nerve agent and allowed it to get into the hands of others”. Mrs May will chair a National Security Council meeting tomorrow.

Jeremy Corbyn called for “robust dialogue” with the Kremlin as a way of dialling down tensions between Russia and the UK.

The White House has said it is closely monitoring the situation and took it “very seriously”.

Speaking on behalf of President Donald Trump, press secretary Sarah Huckabee Sanders said: “Right now we are standing with our UK ally... We certainly stand with them throughout this process. We are ready if we can be of any assistance.”