Police have recovered the source of novichok that killed a woman and left her partner severely ill in Wiltshire, as international chemical weapons investigators travel to Britain.

The nerve agent was found inside a “small bottle” in Charlie Rowley’s home in Amesbury, where he and Dawn Sturgess fell ill almost two weeks ago.

The discovery will allow scientists at the government’s Porton Down defence laboratory to test whether the substance is from the same batch used against Sergei Skripal.

Police are investigating the possibility that the culprit discarded a novichok container that was picked up unwittingly by Ms Sturgess and Mr Rowley four months later.

The British government has invited experts from the Organisation for the Prohibition of Chemical Weapons (Opcw), which previously confirmed novichok was used against the Skripals, to assist the investigation.

They will collect samples to be analysed at designated international laboratories, as efforts to find out where the chemical weapon is from and how it was deployed on UK soil continue.

“The use of chemical weapons is unacceptable and contravenes international law,” a Foreign Office spokesperson said.

“The UK remains committed to upholding the integrity of the Opcw as the implementing body for the Chemical Weapons Convention overseeing the global ban on their use.”

The bottle was found inside Mr Rowley’s home in Muggleton Road, Amesbury (Reuters)

The British government holds Russia responsible for both incidents but the Kremlin has denied any involvement, while its state media has spread conspiracy theories.

Scotland Yard said the bottle of nerve agent was recovered during searches of Mr Rowley’s home in Amesbury on Wednesday and taken to the Defence, Science and Technology Laboratory for tests.

“Scientists have now confirmed to us that the substance contained within the bottle is novichok,” a spokesperson added.

“Further scientific tests will be carried out to try and establish whether it is from the same batch that contaminated Sergei and Yulia Skripal in March – this remains a main line of enquiry for police.

“Inquiries are underway to establish where the bottle came from and how it came to be in Mr Rowley’s house.”

The end of an almost two-week search for the source of contamination will allay public health fears in Salisbury and Amesbury, where police cordoned off several locations visited by the couple before they fell ill on 30 June.

A senior government scientific source previously told journalists including The Independent that the nerve agent could have been smuggled through a British airport in a “discreet” container.

He said the perpetrator of the original attack on Mr Skripal would have to be “highly trained” to deploy novichok without coming into contact with it, possibly wearing protective equipment.

The difficultly of synthesising the chemical, which was first developed by the Soviet Union, and danger of administering it are among the factors cited as indicators of Russian responsibility by the government.

Amesbury major incident after couple exposed to novichok Show all 40 1 /40 Amesbury major incident after couple exposed to novichok Amesbury major incident after couple exposed to novichok Forensic investigators, wearing protective suits, emerge with bagged evidence from the rear of John Baker House in Salisbury, after it was confirmed that two people living in Amesbury had been poisoned with the nerve-agent Novichok. Reuters Amesbury major incident after couple exposed to novichok Dawn Sturgess, a mother-of-three from Durrington, died after being exposed to novichok Facebook Amesbury major incident after couple exposed to novichok British police are scouring sections of Salisbury and Amesbury in southwest England, searching for a container feared to be contaminated with traces of the deadly nerve agent Novichok. Reuters Amesbury major incident after couple exposed to novichok Officers hope that Charlie Rowley, whose partner Dawn died in hospital, can help them establish how the couple came to be contaminated AFP Amesbury major incident after couple exposed to novichok An investigator in a chemical suit works behind screens erected in Rollestone Street PA Amesbury major incident after couple exposed to novichok Fire and Rescue Service personel arrive with safety equipment at the site of a housing estate on Muggleton Road, after it was confirmed that two people had been poisoned with the nerve-agent novichok, in Amesbury Reuters Amesbury major incident after couple exposed to novichok Forensic investigators at John Baker House Reuters Amesbury major incident after couple exposed to novichok Police and military personnel seized a car from a quiet residential street in Swindon as part of their ongoing investigations into the nerve agent incident in Salisbury and Amesbury SWNS Amesbury major incident after couple exposed to novichok Emergency workers in military protective suits search the fenced off John Baker House AP Amesbury major incident after couple exposed to novichok A forensic investigator, wearing a protective suit, emerges from the rear of John Baker House, after it was confirmed that two people had been poisoned with the nerve-agent Novichok, in Amesbury, Britain, July 6, 2018. REUTERS/Henry Nicholls HENRY NICHOLLS Reuters Amesbury major incident after couple exposed to novichok Forensic investigators at John Baker House Reuters Amesbury major incident after couple exposed to novichok Emergency services arrive at John Baker House EPA Amesbury major incident after couple exposed to novichok Dorset Fire and Rescue Service at the house PA Amesbury major incident after couple exposed to novichok Tents set up by search teams are seen at the end of Rollestone Street, outside the John Baker House for homeless people in Salisbury. British police are scouring sections of Salisbury and Amesbury in southwest England, searching for a container feared to be contaminated with traces of the deadly nerve agent Novichok. AP Amesbury major incident after couple exposed to novichok Dorset Fire and Rescue Service at the house in Muggleton Road PA Amesbury major incident after couple exposed to novichok Fire and Rescue Service safety equipment Reuters Amesbury major incident after couple exposed to novichok Police activity at the house in Muggleton Road PA Amesbury major incident after couple exposed to novichok Emergency services arrive at John Baker House EPA Amesbury major incident after couple exposed to novichok Fire and Rescue Service safety equipment PA Amesbury major incident after couple exposed to novichok Police tents are erected outside a residential address in Amesbury, southern England, on July 6, 2018 where police reported a man and woman were found unconscious in circumstances that sparked a major incident after contact with what was later identified as the nerve agent Novichok. Police on July 6, 2018, raced to find the object that contaminated a British couple with the Soviet-made Novichok nerve agent in southwestern England where a former Russian spy was poisoned with the same toxin four months ago. / AFP PHOTO / Chris J RatcliffeCHRIS J RATCLIFFE/AFP/Getty Images CHRIS J RATCLIFFE AFP/Getty Amesbury major incident after couple exposed to novichok Emergency services arrive at the house in Muggleton Road in Amesbury PA Amesbury major incident after couple exposed to novichok Members of the emergency services at the house in Muggleton Road PA Amesbury major incident after couple exposed to novichok Gas masks AFP/Getty Amesbury major incident after couple exposed to novichok Forensic tents outside John Baker House on Rolleston Street, Salisbury, Wiltshire, where counter-terrorism police are investigating after a couple were left in a critical condition when they were exposed to the nerve agent Novichok. PRESS ASSOCIATION Photo. Picture date: Friday July 6, 2018. Dawn Sturgess, 44, and Charlie Rowley, 45, were taken ill on Saturday in Amesbury, around eight miles from where former Russian spy and his daughter were poisoned with the same substance in Salisbury in March. See PA story POLICE Amesbury. Photo credit should read: Yui Mok/PA Wire Sam Blewett PA Amesbury major incident after couple exposed to novichok Fire and Rescue Service personel prepare safety equipment Reuters Amesbury major incident after couple exposed to novichok Police investigators arrive at the site of a housing estate on Muggleton Road Reuters Amesbury major incident after couple exposed to novichok A police officer stands guard behind the housing estate REUTERS Amesbury major incident after couple exposed to novichok Police on the scene Getty Images Amesbury major incident after couple exposed to novichok The couple remain in a critical condition at Salisbury District Hospital AFP/Getty Amesbury major incident after couple exposed to novichok In March Russian former spy Sergei Skripal and his 33-year-old daughter Yulia were poisoned with the Russian-made Novichok in the town of Salisbury. British Prime Minister Theresa May has accused Russia of being behind the attack on the former spy and his daughter, expelling 23 Russian diplomats in retaliation Getty Images Amesbury major incident after couple exposed to novichok British police are cordoning off places the people are known to have visited before falling ill EPA Amesbury major incident after couple exposed to novichok British police officers stand outside a residential property in Amesbury AP Amesbury major incident after couple exposed to novichok Deputy Chief Constable of Wiltshire Police Paul Mills makes a statement to the press outside The Bowman Centre after Wiltshire Police declared the situation a major incident Getty Amesbury major incident after couple exposed to novichok Amesbury Baptist Centre PA Amesbury major incident after couple exposed to novichok Amesbury resident Sam Hobson, speaks to assembled press outside Amesbury Baptist Centre claiming to be a friend of the man and woman exposed to an unknown substance Getty Amesbury major incident after couple exposed to novichok The pair were found unconscious at an address in Muggleton Road, Amesbury Getty Amesbury major incident after couple exposed to novichok Police cordon at Queen Elizabeth Gardens in Salisbury. The town is around 10 miles from Salisbury where former Russian spy Sergei Skripal and his daughter Yulia were poisoned in a suspected nerve agent attack PA Amesbury major incident after couple exposed to novichok Deputy Chief Constable of Wiltshire Police Paul Mills makes a statement Getty Amesbury major incident after couple exposed to novichok Police officers stand outside Boots pharmacy, near to the Barcroft Medical Centre in Amesbury PA Amesbury major incident after couple exposed to novichok Amesbury Baptist Centre PA

Declassified British intelligence states that in the 2000s a covert Russian programme trained agents in “ways of delivering nerve agents, including by application to door handles” – the method used to attack Mr Skripal.

Andrea Sella, professor of inorganic chemistry at University College London, described the bottle found in Amesbury as a “forensic gold mine”.

“Not only is having a significant quantity of sample a real treasure trove to make detailed investigations of the sample, the bottle itself is likely to provide significant clues about its provenance,” she added.

Assistant Commissioner Neil Basu, the head of UK counterterror policing, hailed “a significant and positive development”.

“We cannot guarantee that there isn’t any more of the substance left and cordons will remain in place for some considerable time,” he added.

“This is to allow thorough searches to continue as a precautionary measure for public safety and to assist the investigation team.

“I also appreciate there is a lot of interest in this; however, we are not in a position to disclose any further details regarding the bottle at this stage. The safety of the public and our officers remains paramount.”

Wiltshire police chief constable Kier Pritchard said private security guards would be manning some of the cordons starting next week, following the redeployment of thousands of police officers to guard Donald Trump’s UK visit.

Dawn Sturgess, a mother-of-three from Durrington, died after being exposed to novichok (Facebook)

“This week I’ve been visiting residents of Amesbury and Salisbury and it’s clear that this is a close-knit community that is very much open for business despite the recent challenges they have faced,” he added.

Officials said the risk to the wider public in Wiltshire remains low and no one else has fallen ill in connection with the incident.

Public Health England is maintaining its advice not to pick up “strange items” including syringes, needles, cosmetics or similar objects made of materials such as metal, plastic or glass as a precaution.

Ms Sturgess, a mother-of-three from Durrington, died at Salisbury District Hospital on Sunday evening and police have launched a murder investigation into her death.

A post-mortem is scheduled to take place on Tuesday and an inquest will open and adjourn in Salisbury two days later.

Mr Rowley collapsed hours after his partner on 30 June and was taken to hospital critically ill, but has since regained consciousness and spoke to police for the time on Wednesday.

He remains in a serious but stable condition as 100 counterterror detectives work on the case alongside Wiltshire Police.

“Officers from the investigation team have spoken to Charlie and will be speaking to him further to establish how he and Dawn came to be contaminated,” a spokesperson for the Metropolitan Police said.