A third Russian faces charges over his alleged involvement in the 2018 Salisbury poisonings, which left three people critically ill and one dead.
Prosecutors have authorised charges against Denis Sergeev in the Novichok attack on former double agent Sergei Skripal and his daughter Yulia.
Dawn Sturgess died after the poisoning and a police officer was badly injured.
Police also confirmed they believe the suspects in the case belonged to a Russian military intelligence team.
Security sources believe Sergeev acted as the on-the-ground commander for the operation and was the senior member of the team from Russia’s GRU.
He has also been linked to other covert activity across Europe.
While the Crown Prosecution Service has authorised charges, the suspects cannot be formally charged unless they are arrested.
On 2 March 2018, the alleged GRU hit team came to the UK.
Two men, using the names Alexander Petrov and Ruslan Boshirov, arrived in the afternoon at Gatwick airport. Police have now for the first time confirmed their real names as Anatoliy Chepiga and Alexander Mishkin.
The third man, Denis Sergeev, using the name Sergey Fedotov, had arrived at Heathrow airport earlier that day at 11:00 GMT.
Chepiga and Mishkin travelled to Salisbury on Sunday 4 March, allegedly to smear the military-grade nerve agent Novichok on the handle of former GRU officer Sergei Skripal’s front door.
He and his daughter fell seriously ill as did Nick Bailey, then a police officer.
Sergeev remained in London the whole time before leaving on a flight to Moscow at 13:45, having made a late change to his plans. The other two left on a later fight at 22:30.
Police say they now have evidence the men were operating as a team and that all three met on a number of occasions in London over that weekend.
On some occasions, this was indoors, on others it was in the open air – although the police will not specify exactly where.
The role and identity of Sergeev had been previously disclosed by the investigative site Bellingcat in February 2019 and some of his movements and phone contacts were detailed in a joint investigation with the BBC, including his proximity to Paddington, Oxford Circus and Embankment.
But the police have been working on building up evidence of his role, a process described as “challenging” but which has eventually led to today’s announcement.
“We remain as determined as ever to bring those responsible to justice,” said Dean Haydon, assistant commissioner at the Metropolitan Police and senior national coordinator for counter-terrorism policing.
The charges authorised against the three men are conspiracy to murder, attempted murder, causing grievous bodily harm and use and possession of a chemical weapon.
Chepiga and Mishkin appeared on Russian TV after being identified in 2018 and said they had been to the city simply as tourists to see the cathedral. Russia has always denied any involvement.
Traces of Novichok were found in Chepiga and Mishkin’s hotel room, although none were found in that used by Sergeev.
The Novichok in the perfume bottle could potentially have killed thousands of people, police say.
But there remain significant gaps in the investigation, including how the Novichok came into the UK and where it was between its use in March and its discovery in June in Amesbury in a discarded perfume bottle.
Dawn Sturgess died days after spraying some of the bottle’s contents on herself.
Pre-inquest hearings into her death, presided over by former High Court judge Baroness Hallett, are due to resume this week.
The police are asking the public to get in touch if they have any more details of Sergeev’s movements in London or that of the perfume bottle.
Sergeev, aged around 50, is believed to be in Russia, like the other two suspects. Russia has always said it cannot extradite its citizens.
The UK authorities will inform Interpol to seek his arrest if he does travel outside of the country.
“We now have the evidence that links them to the GRU,” Mr Haydon said. “All three are dangerous individuals.”
Intelligence also links Sergeev and the team to a trail of covert activities across Europe.
Who is the third man?
Sergeev is alleged to be a major general and senior member of Unit 29155 of the GRU, a team tasked with sabotage, subversion and assassination. He joined the team after serving in Russian special forces.
Bulgarian authorities say Sergeev and two other men from Unit 29155 checked into hotels in the capital Sofia in April 2015, insisting on rooms with a view of the underground car park.
Surveillance of that car park released by a Bulgarian prosecutor shows one man approaching the cars of a Bulgarian arms dealer Emilian Gebrev, as well as his son and business partner.
A toxic substance is believed to have been smeared on the handles – similar to the way Novichok was placed on the handle of Sergei Skripal’s house. They would fall ill but survive.
Although he had a return flight booked two days later, Sergeev left the country on 28 April – the day of the poisoning. He may be the man caught on CCTV in the car park.
Chepiga and Mishkin, meanwhile, have been linked to a blast that tore apart an ammunition storage depot used by Emilian Gebrev in a forest in the Czech Republic on 16 October 2014, killing two.
On 11 October 2014, the men used the same cover identities they used in Salisbury – Ruslan Boshirov and Alexander Petrov – to arrive at Prague airport before staying near the depot and then leaving on the day of the explosion.
The accusation by Czech authorities this summer led to a major diplomatic row with Russia and the expulsion of diplomats from a number of countries.
It followed investigative work by European security services who, since Salisbury, have tracked the travel of the three suspects as well as others from the unit to see if they can link it with covert activity.
For Sergeev, this includes visits to Spain, France, Germany, Switzerland and Austria as well as other countries.
He is also believed to have been in touch with members of the GRU unit involved in a planned coup in Montenegro in 2016.
UK police also say they believe the three all travelled to the UK before March 2018. They say they continue to investigate other suspects.