The police have declared a major incident in the town of Amesbury in Wiltshire after two people were found unresponsive.
Police officers on the scene outside Harcourt Medical Centre in Salisbury, thought to be connected to a man and woman in Amesbury who are in the hospital after being exposed to what police confirmed was Novichok.
The man and woman were hospitalized Saturday at Salisbury District Hospital, where authorities initially believed they might have taken a contaminated batch of heroin or crack cocaine.
"We are keeping an open mind as to the circumstances regarding this incident", he told reporters.
Police cordoned off the building and other places the two people visited before falling ill, but health officials said there was not believed to be a wider risk.
Police say specialists have determined that a British couple in their 40s who visited the city of Salisbury were poisoned by the same lethal toxin - developed by the Soviet Union - that nearly killed Sergei and Yulia Skripal in the same English city in March.
"They are both now receiving treatment for suspected exposure to an unknown substance", Wiltshire Police said in a statement.
After being found unconscious in the street, the two spent weeks in critical condition at the hospital.
Sergei and Yulia Skripal have since been discharged from the hospital.
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Britain's interior minister said the nerve agent was the same variety as that used against Skripal and his daughter, but it's not clear whether the two samples came from the same batch. They returned later the same day when a 45-year-old man also fell ill.
The British couple, hospitalized with poisoning earlier this week, were affected by the same strand of "Novichok" nerve agent that was used against Sergei Skripal and his daughter in March, UK Home Secretary Sajid Javid said.
Recent tests, however, suggest the same substance is behind the Amesbury poisoning as the attack on the Skripals, according to police.
"We're satisfied that if anyone was exposed to that level of nerve agent by now they would be showing symptoms."
Prime Minister Theresa May's spokesman said the government's emergency response committee had met to discuss the incident and would meet again on Wednesday evening.
"The public can expect to see an increased police presence in and around Amesbury and Salisbury". They were hospitalized Saturday for suspected drug overdoses. Russian Federation denied any role in the attack on Mr Skripal, a former spy for the United Kingdom, or his daughter but were widely believed by Western powers to be behind them.
They may return, police said.
He said, "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".
Moscow has hit back by expelling Western diplomats, questioning how Britain knows that Russian Federation was responsible and offering its rival interpretations, including that it amounted to a plot by British secret services.