A third Russian faces charges over his alleged involvement in the 2018 Salisbury poisonings, which left three people critically ill and one dead.

Security sources believe Denis Sergeev was the on-the-ground commander 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.

Prime Minister Boris Johnson said that “the suspects should be handed over for justice”.

Russian Foreign Ministry spokeswoman Maria Zakharova said the UK was using the case as “a tool to put pressure on our country”, adding: “We decisively reject all of London’s attempt to blame Moscow for what happened in Salisbury.”

Police confirmed they believe the suspects in the case belonged to a team from the GRU, Russia’s military intelligence service.

Sergeev is believed to be the team’s senior member and has also been linked to other covert activity across Europe.

The Crown Prosecution Service has now authorised charges, but the suspects cannot be formally charged unless they are arrested.

All three suspects are thought to be in Russia.

Nick Price, head of the special crime and counter terrorism division at the CPS, said there was “sufficient evidence to provide a realistic prospect of conviction” and that it was in the public interest to charge Sergeev.

Prosecutors were working with police to bring the attackers to justice “where possible” but Russia has made clear it does not extradite its citizens, he said.

Home Secretary Priti Patel told the House of Commons that if any of the suspects travelled outside Russia, the UK would “take every possible step to detain and extradite them” and would be “relentless in the pursuit of justice”.

She said the poisoning was “an appalling event that shook the entire country and united our allies in condemnation”, but said it was not the first time Russia had committed “a brazen attack in the UK” – referring to the European Court of Human Rights’ judgement on the killing of Alexander Litvinenko.

Analysis: How the UK hopes exposure will deter Russia

None of the three suspects in Salisbury are likely to ever face a British court. Russia has consistently denied any involvement and says it does not extradite its citizens.

This was the same problem UK authorities faced after the killing of Alexander Litvinenko in 2006.

But there are other reasons these investigations matter. The UK’s government response after Litvinenko was seen as weak and falling to do enough to respond and deter Russia.

It now hopes public accusations backed by evidence will help build international pressure on Moscow and encourage other states to also carry out their own investigations.

This year, the revelations about the GRU’s alleged role in a Czech explosion led to the expulsion of diplomats, who were thought to be undercover spies.

The UK and its allies also responded with expulsions after Salisbury and it hopes that exposure and retaliation will disrupt and deter Russia’s ability to carry out such operations overseas.

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.

culled from BBC NEWS