Video report by ITV Meridian's Sally Simmonds (Archive footage courtesy of Porton Down)
The scientist who helped identify the nerve agent used in the Novichok attack, has described the moment he found out the scale of the situation they were dealing with.
Professor Tim Atkins from the defence laboratory at Porton Down says he felt "a mixture of emotions" when he discovered which substance had been used in the incident three years ago.
His reflection comes as the inquest into the Novichok attacks, hears evidence.
When the Novichok attack took place, it was Professor Atkins' job to brief the Chief Constable of Wiltshire Police, Keir Pritchard, who was just days into his new role.
At this time, various parts of Salisbury had been sealed off but no-one had any information about the true scale of the situation.
Professor Tim Atkins said he took a walk around outside and had to have few minutes to really digest what he was being told.
He said: "You go through anger. How can somebody use something so dangerous and so hazardous in an open environment where there are civilians?"
Prof Tim Atkins, Senior Fellow, DSTL:
Once scientists at Porton Down had identified Novichok, they were able to support medics treating Sergei and Yulia Skripal and Detective Sergeant Nick Bailey.
Professor Tim Atkins said: "We are experts at nerve agents, and so we were able to perform a number of activities which slowly moved forward to the position that we were able to make that identification".
Keir Pritchard, Chief Constable of Wiltshire Police, spoke about the moment he was told about the chemical agent.
He said he went through a whole range of emotions, from "anger to worry, through to shock and fear."
"I remember when Professor Tim was describing what he was saying. Just one part of your brain is saying, 'is this really happening'?"
The location of the government defence laboratory at Porton Down, just ten miles up the road from Salisbury, and their expertise in nerve agents was crucial to the investigation.
Work with chemical weapons at the site started in WW2, when Britain wanted to defend itself against German attacks.
Atkins was one of three scientists from DSTL to be given an OBE for their work on Novichok.
Last October, the Queen visited the site to praise their work in 2018, and during the pandemic.