Police are believed to have identified the suspected perpetrators of the Novichok attack on Russian former spy Sergei Skripal.
Officers think several Russians were involved in the attempted murder of the former double agent and daughter Yulia in Salisbury and are looking for more than one suspect.
A source with knowledge of the investigation told the Press Association: “Investigators believe they have identified the suspected perpetrators of the Novichok attack through CCTV and have cross-checked this with records of people who entered the country around that time.
“They (the investigators) are sure they (the suspects) are Russian.”
Investigators are working to the theory that the substance was in a discarded perfume bottle found by Dawn Sturgess, 44, and her partner Charlie Rowley, 45 in a park or somewhere in Salisbury city centre, the source said.
It is thought Ms Sturgess sprayed the Novichok straight on to her skin as it is understood she was exposed to at least 10 times the amount of nerve agent the Skripals came into contact with.
The Metropolitan Police, who are leading the investigation, and the Home Office both declined to comment.
But security minister Ben Wallace wrote on Twitter: “I think this story belongs in the ‘ill informed and wild speculation folder’.”
When asked if the names of the suspects had been run past the Russian authorities, the Prime Minister’s deputy official spokeswoman said: “This is an on-going complex investigation and I can’t comment on the speculation around it.
“We need to make sure the police have the time and space to carry on with the investigation.”
Asked about the latest developments, the Russian ambassador to the UK Alexander Yakovenko told the BBC: “Unfortunately, we don’t have official statement of the British side.
“I want to hear that from the Scotland Yard or from the Foreign Office. A lot of versions that we hear in newspapers, they are not supported by the Foreign Office.”
Ms Sturgess fell ill on the morning of June 30 and died eight days later in Salisbury District Hospital, while Mr Rowley was left fighting for his life after also becoming contaminated.
An inquest into her death was opened by the Wiltshire and Swindon Coroner in Salisbury on Thursday, with her body released to her family for a funeral. It was adjourned until January.
“The cause of death will not be given until further tests are completed,” coroner David Ridley said.
The inquest heard that a “small glass bottle of fluid” containing Novichok had been found at Mr Rowley’s home in Muggleton Road, Amesbury.
Counter-terrorism officers are trying to establish where the container came from, and how it came to be in his house.