Dawn Sturgess and Charlie Rowley were exposed to a contaminated item, say police. (Picture via Facebook).
Police are searching for a "contaminated item" exposed to the nerve agent Novichok which has left a couple fighting for their lives.
Dawn Sturgess and Charlie Rowley were taken ill on Saturday in Amesbury, around eight miles from Salisbury where a former Russian double spy, Sergei Skripal and his daughter Yulia, were poisoned with the same nerve agent in March.
Security Minister Ben Wallace said the latest victims were not directly targeted.
The Defence Science and Technology Laboratory at Porton Down confirmed on Wednesday that the victims had been exposed to Novichok.
Forces personnel were involved in the decontamination efforts following the Salisbury case, but there has no military involvement as of yet following the latest incident.
Police said they cannot rule out more people falling ill as a result of contact with the nerve agent, supposedly left over from the attack on the Skripals.
Home Secretary Sajid Javid MP has accused the Russian state of using Britain as a "dumping ground for poison".
The Kremlin has strongly denied those claims and has accused the Government of trying to "muddy the waters" and "frighten its own citizens".
One theory understood to be under investigation is that Mrs Sturgess and Mr Rawley were poisoned after inadvertently finding a container - such as a phial or syringe - used to transport the nerve agent for the initial attack on the Skripals which was discarded in a public place.
After results from Porton Down confirmed the victims had been exposed to Novichok, the Metropolitan Police said:
"Following further tests of samples from the patients, we now know that they were exposed to the nerve agent after handling a contaminated item," the Met said.
"Detectives are working as quickly and as diligently as possible to identify the source of the contamination.
"Meticulous and systematic searches are under way at a number of sites. The safety of the public and our officers remains paramount and the searches will take longer because of the precautions that we must take to ensure there is no outstanding risk.
"Officers are wearing protective equipment as they carry out their activity and protective barriers may also be installed at some of these sites.
"Cordons remain in place at a number of sites in the Amesbury and Salisbury areas that we believe they visited before they fell ill. This is a precautionary measure while we continue to investigate how they came into contact with the substance."
Although the poisoning of the Skripals may have taken place many months ago, it can remain highly toxic for a considerable amount of time with the smallest trace capable of causing severe illnesses.
Mrs Sturgess and Mr Rowley remain in a critical condition at Salisbury District Hospital.