Former Russian spy Sergei Skripal, his daughter Yulia and police officer Nick Bailey were poisoned with Novichok in Salisbury in March 2018.
Here is a timeline of how events unfolded:
– March 4 2018: Former Russian double agent Sergei Skripal, 66, and his daughter Yulia, 33, are found unconscious on a park bench in Salisbury, Wiltshire.
– March 7: Police say a nerve agent was used to poison the pair and the case is being treated as attempted murder.
– March 8: Then-home secretary Amber Rudd says Wiltshire Police officer Detective Sergeant Nick Bailey is seriously ill in hospital.
– March 12: Then-prime minister Theresa May tells the House of Commons the nerve agent Novichok is of Russian origin and the Government has concluded it is “highly likely” Russia is responsible for the poisoning.
– March 14: Mrs May tells MPs the UK will expel 23 Russian diplomats, calling the incident an “unlawful use of force by the Russian state against the UK”.
– March 22: DS Bailey is discharged from hospital but says life will “probably never be the same”.
– March 26: Britain’s allies announce more than 100 Russian agents are being sent home from 22 countries, in what Mrs May calls the “largest collective expulsion of Russian intelligence officers in history”.
– April 10: Ms Skripal is discharged from hospital, followed by her father just over a month later.
– June 30: Dawn Sturgess and Charlie Rowley fall ill at a flat in Muggleton Road in Amesbury, eight miles from Salisbury, and are taken to hospital.
– July 4: Police declare a “major incident” after revealing Ms Sturgess and Mr Rowley have been exposed to an “unknown substance”, later confirmed to be Novichok.
– July 8: Ms Sturgess dies in hospital after exposure to the nerve agent and a murder investigation is launched.
– July 10: Mr Rowley regains consciousness and is discharged from hospital later that month.
– September 4: Independent investigator the Organisation for the Prohibition of Chemical Weapons confirms the toxic chemical which killed Ms Sturgess was the same nerve agent as that which poisoned the Skripals.
– September 5: Scotland Yard and the Crown Prosecution Service say there is sufficient evidence to charge two Russians, Alexander Petrov and Ruslan Boshirov, with offences including conspiracy to murder over the attack.
– September 12: Russian President Vladimir Putin says there is “nothing criminal” about Petrov and Boshirov. Downing Street insists they are GRU officers “who used a devastatingly toxic illegal chemical weapon on the streets of our country”.
– September 13: Petrov and Boshirov are interviewed by Russian state-funded news channel RT in which they claim they were tourists visiting Salisbury.
– March 1 2019: The Ministry of Defence announces Salisbury is to be declared decontaminated of Novichok after an almost year-long military clean-up of 12 sites.
– June 2020: BBC docudrama The Salisbury Poisonings is broadcast over three consecutive nights. Its first episode was reported to have been watched by more than seven million viewers, making it the biggest UK television premiere of the year so far.
– August 2020: Russian opposition leader Alexei Navalny is treated in hospital in Germany after it was suspected he was poisoned with Novichok.
– March 2021: Three years on from the attack, UK counter-terrorism police say they “remain as determined and committed as ever” to bring those responsible to justice.
– September 2021: Investigators say they have sufficient evidence to charge a third man over the poisonings – Russian spy Denis Sergeev, also known as Sergey Fedotov.