A British police officer who was checked in hospital over concerns he may have been exposed to the deadly chemical Novichok has been given the all-clear.
The officer, believed to be with Wiltshire Police, initially attended Swindon's Great Western Hospital after feeling unwell.
He was later taken to Salisbury District Hospital, a short distance from Amesbury where Dawn Sturgess, 44, and her partner Charlie Rowley, 45, fell ill last Saturday.
They remain in a critical condition in hospital after exposure to Novichok by handling a contaminated item.
A hospital spokesman said: "The police officer who was transferred to Salisbury District Hospital this evening has been tested and does not require any treatment. This individual was not poisoned by a nerve agent.
"The individual has left the hospital site.
Forensic investigators are continuing to comb for clues in Wiltshire after the latest Novichok poisonings - the second major investigation involving the nerve agent this year, following the case of Sergei and Yulia Skripal in March.
Investigators wearing camouflage protective clothing entered the John Baker House assisted-living accommodation in Salisbury, where mother-of-three Dawn Sturgess lives, after they took a sample from the outside of the building on Friday.
Other sites visited by the couple in the lead-up to their hospitalisation are also being looked at, as detectives piece together a timeline of their movements.
Officers have spoken to several key witnesses and are trawling through more than 1300 hours of CCTV footage which has been collected so far.
There is a heavy operational presence at Charlie Rowley's flat, where they were both taken ill.
Incident response vehicles and fire engines joined police at his Amesbury home.
Police have been unable to locate the source of the contamination and have not ruled out the possibility of more people falling ill from coming into contact with the substance left over after the Skripals were targeted.
One theory understood to be under investigation is whether the pair inadvertently found the container used to transport the nerve agent in the Skripal attack.
Charlie Rowley has been described as having foraged for goods to fix and sell, and is known to have collected discarded cigarettes.
Public Health England has repeated "highly precautionary advice" for people who had visited five locations identified by police, but insisted there is no immediate health risk.
Novichok remains highly toxic for a considerable period of time, so even the tiniest trace remaining in a container picked up by the victims could account for their severe illness.