Russia will stand accused of “an unlawful use of force” against Britain if President Vladimir Putin’s officials are unable to prove his agents were not culpable for the deployment of one of the most deadly “military grade” nerve agents ever developed, she said.
Mr Skripal, 66, and Yulia, 33, remain in a critical condition in hospital after coming into contact with Novichok – one of the most dangerous chemicals known to man.
The pair were found slumped on a bench in Salisbury town centre on Sunday, March 4.
Det Sgt Nick Bailey, who went to their aid, remains in a serious but stable condition.
In the Commons yesterday, former Cabinet minister Iain Duncan Smith vowed to back the Prime Minister to take “the most severe action as is required” against Moscow.
He added: “This country, Russia, is now as close to being a rogue state as any. It occupies Crimea, it has helped occupy eastern Ukraine, it has created hell on earth in Syria and is even now overseeing worse action.”
Mrs May described the attack as “an indiscriminate and reckless act against the UK, putting the lives of innocent civilians at risk”.
She promised to take a “full range of appropriate responses against those who would act against our country in this way”.
She added: “We will not tolerate such a brazen attempt to murder innocent civilians on our soil.”
Horrified MPs gasped as the Prime Minister revealed the pair were poisoned with a nerve agent developed in the Soviet Union’s Cold War era chemical warfare laboratories.
Last night White House press secretary Sarah Huckabee Sanders described the poisoning as an “outrage”.
She said: “We offer the fullest condemnation and we extend our sympathy to the victims and their families and our support to the UK Government. We stand by our closest ally and the special relationship that we have.”
Novichok is up to 10 times more lethal than VX – the nerve agent used last year to murder North Korean tyrant Kim Jong-un’s half brother Kim Jong-nam.
Novichok, which means “newcomer”, was developed in the Soviet Union in the 1980s.
Usually applied as an ultra-fine powder, like other nerve agents it acts by blocking the messages from the nerves to the muscles, causing a collapse of many bodily functions.
Effects can take hold within as little as 30 seconds.
Novichok was primarily made because its component parts are not on the banned list from the 1993 Chemical Weapons Convention.
Boris Johnson yesterday summoned the Russian ambassador for a carpeting at the Foreign Office.
There was no handshake between the two men and Mr Johnson is understood to have expressed the British people’s outrage at the reckless disregard for public safety.
He instructed the diplomat to arrange for a full explanation to be given by the end of today.
Updating MPs, Mrs May said there were “only two plausible explanations for what happened in Salisbury”, adding: “Either 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.”
She added: “On Wednesday we will consider in detail the response from the Russian State.
“Should there be no credible response, we will conclude that this action amounts to an unlawful use of force by the Russian State against the United Kingdom. And I will come back to this House and set out the full range of measures that we will take in response.”
Mrs May will convene a gathering of her National Security Council tomorrow to thrash out a response.
The Prime Minister is expected to speak to a string of leaders of Britain’s Nato allies, including Donald Trump, French president Emmanuel Macron and Germany’s Angela Merkel over the coming days to arrange a co-ordinated international response to the crisis.
President Putin yesterday dismissed questions about his state’s alleged involvement in the poisoning, telling a news reporter: “Get to the bottom of things there, then we’ll discuss this.”