The global chemical weapons watchdog has found that "high purity" novichok was used in the attempted murder of former Russian spy Sergei Skripal and his daughter Yulia last month.
Tests carried out by experts from the Organisation for the Prohibition of Chemical Weapons (OPCW) showed the nerve agent was found in environmental samples collected in Salisbury.
Blood tests also revealed that the chemical was found in blood samples taken from the Skripals and Detective Sergeant Nick Bailey, the police officer who first attended the scene.
The report from the OPCW said the chemical was "high purity" with a complete absence of contaminants.
The UK believes it is highly likely that the Russian State orchestrated the attack.
However the country’s chemical weapons research facility has admitted that, while it can confirm novichok was the substance used, it cannot tell where it was manufactured.
Novichok is a military-grade nerve agent developed by Russia from the 1970s onward, however the country’s president Vladimir Putin has warned that it could be produced in up to 20 countries.
UK Foreign Secretary Boris Johnson called the results "conclusive," despite the fact the OPCW offered no opinion on who carried out the attack.
"There can be no doubt what was used and there remains no alternative explanation about who was responsible - only Russia has the means, motive and record," he said.
The tests were carried out by four independent laboratories affiliated with OPCW and samples were transported under a "full chain of custody," the report said.
It did not name novichok directly but said: "The results of the analysis by the OPCW designated laboratories of environmental and biomedical samples collected by the OPCW team confirms the findings of the United Kingdom relating to the identity of the toxic chemical that was used in Salisbury and severely injured three people."
The OPCW was tasked with identifying the chemical, not with attributing its origin or ascertaining blame for the poisoning.
Russia earlier this month lost a bid to be included in the watchdog's investigation.
Responding to the report, Britain called a session of the OPCW to discuss next steps.
"We will now work tirelessly with our partners to help stamp out the grotesque use of weapons of this kind," Boris Johnson said in his statement.
"The Kremlin must give answers. We must, as a world community, stand up for the rules based order which keeps us all safe. The use of weapons of this kind can never be justified, and must be ended."
Nearly a month after the pair were found unconscious on a bench in Salisbury, Yulia Skripal has been discharged from hospital and her father Sergei is no longer in a critical condition.
