By Agence France-Presse
Amesbury, United Kingdom
Counter-terrorism police are now leading the investigation into the incident after tests at the Porton Down defence laboratory confirmed the nature of the substance, which Britain says is a Soviet-made military grade nerve agent.
"It's the same nerve agent. Whether we can ever tell if it's the same batch will be up to scientists to determine," Neil Basu, head of counter-terrorism police, told reporters.
"The priority for the investigation team now, is to establish how these two people have come into contact with this nerve agent," he said.
Basu said there was no evidence to suggest that the man and the woman, named locally as Charlie Rowley and Dawn Sturgess, "were targeted in any way".
The two fell ill on Saturday in Amesbury in southwestern England, close to where former double agent Sergei Skripal and his daughter Yulia collapsed on a bench on March 4 in an incident that sparked a bitter diplomatic crisis with Russia.
"The possibility that these two investigations might be linked is clearly a line of enquiry for us," Basu said.
'Low risk' to public
But Basu said there was no evidence the man and the woman had "recently visited any of the sites that were decontaminated" after the poisoning of the Skripals.
"This remains a low risk to the general public," he said.
"We're satisfied that if anyone was exposed to that level of nerve agent by now they would be showing symptoms."
The 44-year-old woman collapsed first and an ambulance was called at around 0915 GMT, while the 45-year-old man fell ill later and an ambulance was called at 1430 GMT.
Police had initially assumed that the two had consumed a contaminated batch of drugs.
But samples from both patients were sent to Porton Down on Monday "due to concern over the symptoms the man and woman were displaying," Basu said.
Both are still in a critical condition and are at Salisbury District Hospital -- the same facility where the Skripals were treated.
Local man Sam Hobson, 29, told AFP he was a friend of the pair and said he saw the man fall ill.
"He was sweating loads, dribbling, and you couldn't speak to him, he was making funny noises and he was rocking backwards and forwards," Hobson said.
"It's like he was in another world."
Home Secretary Sajid Javid said he would be chairing an emergency cabinet meeting on Thursday on the case and a spokesman for Prime Minister Theresa May said she was being "regularly updated" on the situation.
- Helplines for residents -
In Salisbury, local residents said they were "shocked" that their quiet area was again hitting the headlines.
"I was shocked to hear that something had happened so soon after the last contamination scare," Patrick Hillman, 70, told AFP.
The Skripal poisoning "really affected business and life in general in Salisbury" in recent months, he said.
"It is a bit of a scare," said John Reid, 84.
Police launched two helplines for those worried about possible contamination.
"We cannot underestimate the impact the shocking news of a second major incident in this part of our county in such a short space of time will have," Wiltshire Police Chief Constable Kier Pritchard said in a statement.
Police called for calm but also said that anyone who had visited any of the five sites that the man and the woman went to on Friday and Saturday should wash clothing worn at the time and wipe down personal items.
The sites, which have now been cordoned off, are a park and a homeless hostel in Salisbury, as well as a pharmacy, a church and the house in Amesbury.
- 'Such a quiet place' -
Local resident Natalie Smyth, 27, told AFP she saw fire engines and ambulances arrive at the house on Saturday.
"They shut the road. They said it was a chemical incident and then that it was drug-related.
"It is so strange, it is such a quiet place," she said, indicating that the emergency services personnel were wearing protective suits.
The police said local residents should expect to see officers in protective suits at "a number of sites" in the coming days.
Skripal, 67, and his 33-year-old daughter Yulia, who was visiting from Moscow, collapsed on March 4 in Salisbury and were treated for an extended period of time before being released from hospital.
A police officer who came to their aid, Nick Bailey, was also taken to hospital.
The police said they suspected the nerve agent may have been smeared on a front door handle in liquid form.
Moscow has rejected British accusations of involvement in the Skripal poisoning, which sparked a diplomatic crisis that saw Russia and the West expelling dozens of diplomats in tit-for-tat moves.