Novichok scientist Vil Mirzayanov warns of 'irreversible' damage caused by weapon

A scientist who helped test the lethal nerve agent Novichok for the Russian military has warned that the poison can cause "irreversible damage" to the nervous system even if victims survive.

Vil Mirzayanov helped synthesise the Novichok agent, said to be the substance used to poison Sergei Skripal and his daughter Yulia, in Moscow's GosNIIOKhT military chemical weapons laboratory.

He said the Skripals may have come into contact with a non-lethal dose as he explained as little as 1mg of the substance can kill one person and 1g can kill 1,000.

Ms Skirpal and Detective Sergeant Nick Bailey, who was also treated for symptoms following the incident in Salisbury, have now been released from hospital.

But Mr Mirzayanov warned they should be permanently monitored by doctors as the nerve agent causes long-term damage to the nervous system.

He said he only knew one person, his friend Andrei Zheleznyakov, who survived coming into contact with the substance but he died five years later.

"We tried to cure him but he wasn't cured entirely," he said. "It causes irreversible damage to the nervous system."

He described the Novichok series as a "weapon for the Soviet army" that is "not used on the battlefield".

He described symptoms of a tiny dose including a narrowing of the pupils, vision loss, vomiting, trouble breathing, paralysis and convulsions before leading to a lethal result if an antidote is not injected.

He said he would tell doctors: "Be cautious don't celebrate this victory...because some damage should be irreversible, we have to look at the future circumstances."

Mr Mirzayanov, who tested the substance on animals, said that he felt guilty for his contribution to the development of the agent.

"I apologise that I was participating in the creation of this agent, because of that I am also guilty," he said. "I never imagined this work would be used for such a terrible cause."

Mr Mirzayanov now lives in exile in the US after he blew the whistle on weapon stockpiles in the Soviet Union in the 1990s.