Former Russian double agent Sergei Skripal and his daughter were poisoned with Novichok in Salisbury three years ago on Thursday.

PA looks at 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.

– 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

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 was 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

UK counter terrorism police say they “remain as determined and committed as ever” to bring those responsible for the Salisbury attack to justice.