Russian double agent critical after suspected poisoning on UK soil

A former Russian intelligence agent is fighting for his life in the UK after a suspected poisoning.

The spy, Sergei Skripal, was a double agent who worked for Britain, passing on Russian state secrets before being found out and sent to prison for treason.

He was sent back to the UK during a prisoner transfer in 2010 and was discovered poisoned in a park on Monday (local time).

Every precaution is being taken by forensic officers in Salisbury, England as they sift piece by piece through one of the park's rubbish bin, searching for traces of deadly poison.

A woman in her 30s and 66-year-old Skripal were found unconscious on a park bench near the bin.

"There was a couple, an older guy and a younger girl. She sort of leant in on him, it looked like she'd passed out maybe," said witness Freya Church.

"He was doing some strange hand movements, looking up to the sky.

"I felt anxious, I felt like I should step in but to be honest they looked so out of it that I thought that even if I did step in I wasn't sure how I would help."

A major incident was declared and a local restaurant closed as a precaution - all signs pointing to poison.

"The pair, who we believe are known to each other, did not have any visible injuries and were taken to Salisbury district hospital," said Chief Constable Craig Holden from Wiltshire police.

"They are currently being treated for suspected exposure to an unknown substance. Both are currently in a critical condition in intensive care."

Skripal was arrested in 2004 in Russia and convicted of treason. He was sentenced to 13 years' prison for exposing state secrets.

In 2010 - as part of a high-profile prisoner swap in Vienna - he was released to the UK, exchanged for 10 Russian agents.

"This has not been declared as a counter-terrorism incident and we would urge people not to speculate," said Const Holden.

"However, I must emphasise that we retain an open mind and we continue to review this position."

It wouldn't be the first time a former Russian spy was poisoned on UK soil.

In 2006, Alexander Litvenenko was killed by radioactive poison after drinking tainted tea.

A British inquiry found it was likely on Russian President Vladimir Putin's orders.

Newshub.