Video report by ITV News Wales Correspondent Rupert Evelyn
Police teams investigating the latest poisoning in Salisbury have revealed more details of the movements of the two victims before they fell ill.
Mother-of-three Dawn Sturgess and Charlie Rowley remain in a critical condition as searches continue at his assisted-living home in Amesbury.
Forensic investigators in camouflage hazardous material suits were seen entering John Baker House, which has been evacuated, shortly after 3pm.
A sample was also taken from a windowsill at the accommodation.
Detectives released details of their movements on Friday and Saturday after speaking to key witnesses and trawling through more than 1,300 hours of CCTV footage.
They issued the following timeline:
At around 12:20pm on Friday Mr Rowley and Ms Sturgess are together at John Baker House in Salisbury before leaving and visiting several shops, then heading to Queen Elizabeth Gardens.
They return to John Baker House at around 4.20pm before catching a bus to Amesbury at approximately 10.30pm. Detectives currently believe they spent the night at an address on Muggleton Road, Amesbury.
On Saturday ambulance crews called on the address at 10:15am, where Ms Sturgess had been taken ill and took her to hospital.
At around midday, Mr Rowley visited Boots the chemist on Stonehenge Walk in Amesbury and then returned to his address in Muggleton Road around half an hour later.
At around 1.45pm he visited the Amesbury Baptist Centre on Butterfield Drive and returned home at around 3pm.
At 6.20pm the South West Ambulance Service were called back to the address on Muggleton Road and Mr Rowley was taken to hospital.
The pair came into contact with the same novichok nerve agent used in an attack in nearby Salisbury four months earlier.
Police have been unable to locate the source of the contamination and have not ruled out more people falling ill from coming into contact with the substance left over from the attempted murder of Sergei and Yulia Skripal.
Wiltshire residents were warned to expect investigators descending on the scenes, while other cites the couple were known to have visited before being taken ill are behind cordons.
How did Charlie Rowley and Dawn Sturgess come into contact with novichok?
One theory understood to be being investigated is whether the pair inadvertently found the container used to transport the nerve agent in the Skripal attack before being recklessly discarded.
Mr Rowley has been described as having foraged for goods to fix and sell and is known to have collected discarded cigarettes.
CCTV showed Dawn Sturgess shopping in Salisbury before falling ill
Footage emerged of Ms Sturgess the day before she was rushed to hospital after being exposed to the nerve agent.
In the CCTV footage obtained by ITV News, Ms Sturgess can be seen buying alcohol in 'Charlie's Store' at Old George Mall in Salisbury on Friday afternoon, close to the location where Sergei and Yulia Skirpal were poisoned by novichok in March.
Images show Ms Sturgess - wearing a long dress and straw hat - entering the store with a friend.
Video report by ITV News Correspondent Dan Rivers
The next day, both Ms Sturgess and Mr Rowley were found displaying worrying symptoms at Mr Rowley's flat in Muggleton Road in Amesbury, around eight miles from where the Skripals were poisoned.
The Metropolitan Police say detectives are "working as quickly and as diligently as possible to identify the source of the contamination".
A friend of the couple, Sam Hobson, told ITV News that he called an ambulance on Saturday after Mr Rowley began foaming at the mouth.
"It's obviously something that they touched [that has made the pair ill] and they've got infected by it so they're getting enzymes pumped through them in the hospital, same as the other people did last time," he said.
Wiltshire Police initially thought the couple had taken contaminated crack cocaine or heroin, however after samples were sent to the chemical weapons research laboratory at Porton Down, it was revealed that they had been exposed to the nerve agent novichok.
Metropolitan Police Assistant Commissioner Neil Basu said it is not thought the individuals are linked in any way to Russia or to the Skripals but Home Secretary Sajid Javid said he "cannot rule out" the possibility the novichok found in Amesbury was from the same batch used in the Salisbury attack.
Mr Javid called on Russia to "come forward and (explain) 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".
And 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."
The Amesbury incident will raise "serious questions" over the multi-million pound decontamination operation that was carried out in Salisbury following the March attack, a Government source told the Press Association.
Novichok, which is the name for a family of nerve agents, was developed by the Soviet Union in the 1970s and 1980s and was said to be the world's most powerful nerve agent.