The former Russian double agent 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.

“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.