The former Russian double agent, Sergei Skripal, and his daughter poisoned by a deadly nerve agent will either die or be crippled by their exposure to Novichok, according to the whistleblower who alerted the world to Russia's secret chemical weapons programme.
Vil Mirzayanov, a chemist who worked at the heart of the Soviet programme, said Russia was the only country able to produce and deploy such a powerful nerve agent, and he warned that many more people may fall ill, The Telegraph reported.
"It is at least 10 times more powerful than any known nerve agent. Plus practically it is incurable," he said at his New Jersey home on Monday evening.
"These people are gone – the man and his daughter. Even if they survive they will not recover. That is the terrible damage it does.
"I'm afraid many more people were exposed."
He added that he believed the poison used in the Salisbury attack would have been manufactured in Russia as two, harmless components. They would have been brought into the UK and then combined inside a tiny, easily hidden aerosol spray that could be used to deliver a deadly dose and a "deliberate demonstration" to Moscow's enemies around the world.
He spoke hours after Theresa May gave Vladimir Putin until the end of Tuesday to explain the use of Novichok or face retaliation.