Police hunting the Novichok nerve agent after an attack on a former Russian spy have suffered hypothermia, a counter-terrorism forensics chief has said.

Former spy Sergei Skripal, his daughter Yulia and then police officer Nick Bailey were poisoned with Novichok in Salisbury in March 2018. They all survived, however Dawn Sturgess, 44, died four months later when was exposed to the chemical in nearby Amesbury.

Keith Asman, head of forensics and digital investigations for the South East regional counter-terrorism unit, said officers were working in “extreme weather”.

He said it was an incredibly difficult task, “like looking for a needle in a haystack” without knowing what the needle was.

Mr Asman told the Dawn Sturgess Inquiry on Thursday that they did basic blood tests on forensic staff to ensure they were not contaminated because of how dangerous the work was.

Mr Skripal and his daughter fell ill after being contaminated by Novichok found on the front door handle of his home in Salisbury. Mr. Bailey was also subsequently poisoned.

Mrs Sturgess, a mother-of-three from Wiltshire, died after spraying herself with Novichok, which had been contained in a discarded perfume bottle. It had been found and given to her by her boyfriend Charlie Rowley.

The inquest heard that senior police officers wanted to trace the nerve agent container after the poisoning of the Skripals.

He said, “I was looking for a needle in a haystack.

“I didn’t know what the needle looked like, nor where the hay wagon was, nor if it was even in the country.

“We had absolutely no idea what we were looking for.”

March 2018 saw periods of very severe weather, including Storm Emma and periods of heavy snow.

Mr Asman said: “We were working in extreme weather conditions so officers got sick from hypothermia because when they left the premises in a hot environment with PPE they would go out and undress safely in a area where he was. snow, although we had tents above us”.

Mr Asman, whose previous work cases included the poisoning of former Russian spy Alexander Litvinenko and the 7/7 London bombings, said officers looked around flower pots and drains around Mr Skripal’s home before expanding the search area.

He explained that during a subsequent search in the summer after Ms Sturgess fell ill in June 2018, officers then collapsed with heat exhaustion from the PPE.

The investigation continues.