UK calls on Russia to give details after couple left critical following exposure to Novichock nerve agent
Counter-terror police say pair were exposed to the same nerve agent as former Russian spy Sergei Skripal and his daughter Yulia earlier this year.
Britain's security minister called on Russia to give details about the Novichok nerve agent attack on a former double agent and his daughter after two British citizens were poisoned with the same substance.
The two Britons are critically ill after what is thought to be a chance encounter with the poison after the March attack on former Russian agent Sergei Skripal and his daughter Yulia in Salisbury in March.
Britain has accused Russia of the poisoning of the Skripals, a charge Russia has repeatedly denied.
"The Russian state could put this 'wrong' right, they could tell us what happened, what they did and fill in some of the significant gaps that we are trying to pursue," Security Minister Ben Wallace told BBC radio on Thursday.
"They (Russia) are the ones who could fill in all the clues to keep people safe."
The couple, named locally as mother Dawn Sturgess and Charlie Rowley, were discovered in Amesbury, around eight miles from where the Skripals were poisoned with Novichok in March.
It came as Downing Street confirmed Home Secretary Sajid Javid will chair a meeting of the Cobra emergency committee on Thursday.
Speaking to reporters from New Scotland Yard, Metropolitan Police Assistant Commissioner Neil Basu said police were investigating links between the two poisonings.
He said: "I appreciate that there will be a great deal of speculation as to whether this incident is linked to the events in Salisbury in March.
"I would add that the complex investigation into the attempted murders of Yulia and Sergei remains ongoing and detectives continue to sift through and assess all the available evidence and are following every possible lead to identify those responsible, for what remains a reckless and barbaric criminal act.
"I must say that we are not in a position to say whether the nerve agent was from the same batch that the Skripals were exposed to. The possibility that these two investigations might be linked is clearly a line of enquiry for us."
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Professor Dame Sally Davies, chief medical officer for England, said the Skripal episode meant officials had a "well-established response" in place.
She said: "I understand that those in Salisbury and in surrounding areas will be concerned at this news, particularly those who recently visited areas now cordoned off by police."
She said the risk to the public remains low but issued "highly precautionary" advice to those with concerns.
Officers were called to a home in Muggleton Road, Amesbury, on Saturday morning when the 44-year-old woman collapsed. They were called back later that day when the man, 45, also fell ill.
Wiltshire Police initially thought that the couple had taken contaminated crack cocaine or heroin, but then decided to carry out further tests and on Wednesday declared a major incident.
Cordons remained in place in areas the pair were known to frequent in Amesbury and in Salisbury, including Queen Elizabeth Gardens and Amesbury Baptist Centre where it is believed they were last seen in public at a family fun day on Saturday.
Mr Basu said: "We have cordoned off a number of sites in the Amesbury and Salisbury areas that we believe the two individuals visited in the period before they fell ill.
"This is a precautionary measure while we continue to investigate how they came into contact with the substance.
"I do want to reassure the public, however, that there is no evidence that either the man or woman recently visited any of the sites that were decontaminated following the attempted murders of Sergei and Yulia Skripal."
He said people in the area could expect to see "an increased police presence" in the coming days.
Amesbury Baptist Centre secretary Roy Collins said the pair were among 200 who attended an event on Saturday and they were not regulars.
"Last weekend we held a community fundraiser and we understand this may well be the last event this couple went to in public," he said.
"We are all quite puzzled and shocked - naturally the connection with Salisbury and recent events there mean there is a heightened public interest."
Public Health England (PHE) said it did not believe there to be a "significant health risk" to the wider public, although its advice was being reviewed.
The address where the couple were found is on a new housing development on the southern edge of the town, which lies close to Stonehenge.
Neighbours living near the scene were keen to find out more about what had happened to the couple.
College student Chloe Edwards, 17, described seeing police cars, fire engines and people in "green suits" on Saturday night.
"We were just eating our dinner and all these emergency vehicles turned up," she said.
"They were putting on these green suits and we thought it was the gas as our electricity was turned off as well."
She said the vehicles arrived at about 7pm and she and her family were told to stay inside their home until about 10pm.
"We wanted to know what happened and, with the Russian attack happening not long ago ... we just assumed the worst," she said.