How does Theresa May know it was Russia?

 From counterpunch.org:

Darling Nikki Haley’s clearly pissed that she was passed over for Secretary of State. She went rogue on Wednesday by grinding on the Russians over the poisoning of Sergei Skripal and his daughter Yulia.  Skripal is a Russian exile and double agent. In a rabid speech before the UN, Haley reiterated British PM Theresa May’s accusation that the Skripals were poisoned with the highly toxic “Novichok” nerve agent manufactured by the Russian government.

May offered no evidence for her charge. Salisbury is just a few miles down the road from the UK’s very own chemical weapons facility at Porton Down. The Soviet’s Novichok program was tested at a research base in Nukus, Uzbekistan, which ultimately fell into US hands after the former Soviet Republic gained its independence. One of the chemists who helped develop the Novichok poisons, Vil Mirzayanov, left Russia to live in the US. The US was charged with decommissioning the facility and destroying any stockpiles of chemical and biological weapons. So both the Brits and the US may have had access to Novichok, as well as any number of independent actors who could have bought the chemical on the black market.

How the UK identified the poison as a Novichok agent remains a mystery, since British researchers at Porton Down allegedly don’t have any samples and the Organisation for the Prohibition of Chemical Weapons Scientific Advisory Board (OPCW) claims that it has “insufficient information” to accurately detect and identify Novichok agents. No wonder Jeremy Corbyn warned that May had prematurely, and dangerously, leapt to blame the attack on the Russian government. Corbyn decried the “McCarthyite” hysteria sweeping Britain and sagely urged people to “keep calm.”