A team from the Organisation for the Prohibition of Chemical Weapons (OPCW) will collect samples
International chemical weapons investigators will arrive in the UK on Monday in the wake of the Salisbury nerve agent attack.
Former Russian spy Sergei Skripal (66) and his daughter Yulia (33) were found unconscious on a bench in Salisbury two weeks ago, with local investigators since determining a nerve agent was used in the 'attempted murder' of the Skripals.
A British police officer also remains in a serious condition following the incident.
British officials have accused Russia of being responsible for the attack - either by directly ordering the attack, or through having 'lost control' of Soviet Union developed nerve agents known as novichok.
Russia has denied the allegations, while other countries such as the US have backed the UK's assessment.
Today, the British Foreign Office confirmed a team from the Organisation for the Prohibition of Chemical Weapons (OPCW) in The Hague will begin their investigation tomorrow.
They are due to collect samples, with subsequent test results expected to take at least two weeks.
In a statement, the UK's Foreign Office said: "The Foreign Secretary [Boris Johnson] revealed this morning that we have information indicating that within the last decade, Russia has investigated ways of delivering nerve agents likely for assassination. And part of this programme has involved producing and stockpiling quantities of novichok. This is a violation of the Chemical Weapons Convention.
"The start of the investigation by the international chemical weapons watchdog comes as the Foreign Secretary travels to Brussels to brief foreign ministers from across the European Union on the attempted assassinations in Salisbury before meeting with the NATO Secretary General."
Yesterday, Russia confirmed it is to expel 23 British diplomats within a week, in response to the UK expelling 23 Russian diplomats following the Salisbury attack.
Boris Johnson has said it is "overwhelmingly likely" that Russian President Vladimir Putin - who is set to be re-elected following an election in Russia today - signed off on the attack.
However, Russian Foreign Minister Sergei Lavrov called Mr Johnson's claims "shocking and unforgivable".
One of the alleged targets of the Salisbury attack, Sergei Skripal, was convicted in Russia in 2006 of passing state secrets to Britain.
He was later given refuge in the UK as part of a spy swap.