A third Russian agent who travelled to the UK during the Salisbury attack may have commanded the men who poisoned Sergei Skripal, researchers have found.

The investigative website Bellingcat said mobile phone records showed that Denis Sergeev, who used the cover name Sergey Fedotov, may have met the two agents who carried out the attempted assassination in London.

Sergeev was first identified as a senior GRU officer in February, and sources told the BBC he holds the rank of major-general.

After uncovering a record of involvement in prior international operations, Bellingcat concluded that he was “likely in charge of coordinating the Salisbury operation”.

Researchers said the available evidence indicated “he was involved in the Skripal operation in a supervising, coordinating role; communicating back and forth to Moscow, while leaving the suspected hit-team to work in an operational ‘Faraday cage’.”

Telephone records obtained from a whistleblower at a Russian mobile operator showed Sergeev lived in Moscow and worked at GRU buildings including its headquarters and academy.

The phone number, registered under his cover name, was used to book flights to London on 1 March 2018 and he arrived at Heathrow Airport the following morning – four hours ahead of GRU agents Alexander Mishkin and Anatoliy Chepiga.

Bellingcat said he travelled to a hotel near Paddington railway station in west London and “barely left” for the next two days.

He was exchanging messages on encrypted apps including Telegram, Viber and WhatsApp and downloading large files – all using mobile networks rather than wifi – and speaking on the phone to someone codenamed “Amir from Moscow”.

On 3 March, Sergeev made his only known journey out of the Paddington area and his phone registered near Oxford Circus and Embankment.

He was in the Embankment area between noon and 1.30pm – the same period when Mishkin and Chepiga were about to catch a train to Salisbury from nearby Waterloo station.

The Metropolitan Police said the pair arrived in the area at 11.45am but their train did not leave until 12.50pm. With only a 10 minute walk between Waterloo and Embankment, the three agents could have met in that time.

“Had a meeting in person been necessary between Sergeev and the Chepiga/ Mishkin team – whether to pass on final instructions or a physical object – the area between the Embankment and the Waterloo would have been a convenient place, and the one-hour time gap between their arrival to the station and their departure would have likely sufficed,” Bellingcat said.

Chepiga and Mishkin then made their first trip to Salisbury, on what police said was a reconnaissance mission.

On 4 March they returned, spreading novichok on Skripal’s front door and causing the former double agent and his daughter to fall critically ill.

They and a police officer who visited the home recovered following hospital treatment but a local woman, Dawn Sturgess, died in July 2018 after her partner mistakenly gave her novichok concealed in a counterfeit perfume bottle as a gift.

Sergeev exchanged a total of 11 calls with “Amir” during the course of the trip, including on the evening before the poisoning and shortly before the would-be assassins left for Salisbury on 4 March.

He left London on the morning of 4 March, journeying to Heathrow for a 1.30pm flight to Moscow, nine hours before the poisoners flew out on the same route.

The number used by Sergeev belonged to a prepaid SIM card without a documented owner – a violation of Russian rules – and did not produce a normal footprint because it did not produce cell tower logs.

“It is thus likely that this is a number from a special series used by Russian’s security services,” Bellingcat concluded.

“The new findings confirm that Sergeev was an active GRU officer at the time of the Salisbury operation, as opposed to a retired officer employed for a private operation.

“They also shed light on the likely chain of command for this (and other) GRU overseas operations, with one coordinating senior officer communicating with headquarters in Moscow while the team on the ground receive limited to no new instructions.

“This set-up may be linked to operational security and the need to minimise the operative team’s exposure to traceable data communications.”

Appearing on the government-owned RT news network after being named under their cover identities, Chepiga and Mishkin denied involvement and claimed they were nutritional supplement salesmen who were on holiday in London.

Chepiga, posing as Boshirov, said friends suggested visiting the “wonderful town” because of its “internationally famous” cathedral, known “for its 123m spire”.

Scotland Yard officers are still investigating the attack, after charging Chepiga and Mishkin with conspiracy to murder and novichok possession in September, and have not confirmed or denied the existence of other suspects.

“The investigation team continues to pursue a number of lines of enquiry, including identifying any other suspects who may have been involved in carrying out or planning the attack,” a spokesperson said.

“We are not prepared to discuss further details of what remains an ongoing investigation.”

Sajid Javid has admitted that as Russia will not extradite the suspects and they can only be detained if they enter a nation that complies with European Arrest Warrants and Interpol red notices, catching them is unlikely.

“If they ever step out of the Russian Federation, Britain and its allies will get them and we will bring them to prosecution,” the home secretary vowed.

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