Britain is is in danger of becoming a “dumping ground for poison”.
The stark warning from Home Secretary Sajid Javid comes as it emerged the couple left in a critical condition in Wiltshire were exposed to the same nerve agent as as former Russian spy Sergei Skripal and his daughter Yulia.
The pair, named locally as mother Dawn Sturgess and Charlie Rowley, were taken ill on Saturday in Amesbury, around eight miles from where the Skripals were poisoned with Novichok in Salisbury.
Mr Javid has now called on Russia to provide a proper explanation for both incidents in Salisbury.
He told MPs: “The eyes of the world are currently on Russia, not least because of the World Cup.
“It is now time that the Russian state comes forward and explains exactly what has gone on.”
He accused Moscow of working to undermine UK and international security, saying “we will stand up to the actions that threaten our security”.
He added: “It is completely unacceptable for our people to be either deliberate or accidental targets, or for our streets, our parks, our towns, to be dumping grounds for poison.”
Mr Javid said that more than 100 counter-terrorism detectives were working on the case.
He said the risk to the public remained low, adding: “We have taken a very robust approach to decontamination and there is no evidence that either the man or the woman in hospital visited any of the places that were visited by the Skripals.”
Shadow home secretary Diane Abbott warned that British streets must not be allowed to become “killing fields for state actors”.
She told the Commons: “We cannot allow the streets of ordinary British towns and communities to become killing fields for state actors.”
It is understood investigators are working on a theory that the pair came into contact with the deadly substance in a part of Salisbury city centre that was outside the clean-up launched after the attack against the Skripals.
A senior Government source said it is believed there was cross-contamination of the same batch of nerve agent involved in the ‘reckless’ Salisbury attack, as opposed to a secondary attack.
The source told the Press Association: ‘They [the authorities] have never been able to ascertain the item used to deposit the Novichok and it’s possible the pair have come into contact with that item.’
Test results from the Government’s Porton Down laboratory came back at 7pm on Wednesday confirming the substance was Novichok.
Security minister Ben Wallace said the victims were not deliberately targeted.
Mr Wallace told BBC Radio 4’s Today programme: ‘The working assumption would be that these are victims of either the consequence of the previous attack, or something else, but not that they were directly targeted.’
Linking the incident to the attack on the Skripals, Mr Wallace said: ‘I think what we said at the time was that this was a brazen and reckless attack in the heart of a very peaceful part of the United Kingdom, and that is part of the anger I feel about the Russian state is that they chose to use clearly a very, very toxic, highly dangerous weapon.’
Mr Wallace called on Moscow to provide information, saying: ‘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.
‘We have said they can come and tell us what happened. I’m waiting for the phone call from the Russian state. The offer is there. They are the ones who could fill in all the clues to keep people safe.’
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.’
Professor Dame Sally Davies, chief medical officer for England, said the Skripal episode meant officials had a ‘well-established response’ in place.
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.
Sam Hobson, a friend of the pair, said he visited the park with them on Friday evening.
He told The Guardian that, after Ms Sturgess was taken to hospital on Saturday morning, he accompanied Mr Rowley to a Boots chemist in Amesbury before the pair attended a free hog roast at a local baptist church.
Meanwhile Amesbury Baptist Centre secretary Roy Collins said the couple were among 200 who attended an event on Saturday and they were not regulars.
Public Health England 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.