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’”.

Police release images of suspects in connection with Salisbury attack Show all 19 1 /19 Police release images of suspects in connection with Salisbury attack Police release images of suspects in connection with Salisbury attack CCTV – Salisbury train station The two suspects charged in relation to the attack on Sergei and Yulia Skripal at Salisbury train station at 16:11hrs on 03 March 2018 Metropolitan Police Police release images of suspects in connection with Salisbury attack Suspects Suspects Ruslan Boshirov and Alexander Petrov, Russian nationals, approximately 40 years old, who travelled on a Russian passport. It is likely that they were travelling under aliases and that these are not their real names Metropolitan Police Police release images of suspects in connection with Salisbury attack Evidence Bottle and applicator recovered by police from Charlie Rowley’s address in Muggleton Road Metropolitan Police Police release images of suspects in connection with Salisbury attack Evidence A counterfeit perfume box that was discovered by nerve agent victim Charlie Rowley, who later gave it, and the bottle inside, to his girlfriend Dawn Sturgess Metropolitan Police/AFP/Getty Police release images of suspects in connection with Salisbury attack Rowley has previously said he felt lucky to be alive after giving a perfume bottle that contained the nerve agent Novichok to his girlfriend Dawn Sturgess, who later died Metropolitan Police/AFP/Getty Police release images of suspects in connection with Salisbury attack Suspeccts The CPS has issued European Arrest Warrants for the extradition of 'Boshirov' and 'Petrov' in connection with the Novichok poisoning attack on Sergei Skripal and his daughter Yulia in March Metropolitan Police/PA Police release images of suspects in connection with Salisbury attack CCTV – ‘Boshirov' at Gatwick airport Movements in detail - At 3pm on Friday, 2 March, the suspects arrived at Gatwick airport, having flown from Moscow on Aeroflot flight SU2588 Metropolitan Police Police release images of suspects in connection with Salisbury attack CCTV – ‘Petrov’ at Gatwick airport From the airport it is believed that they travelled by train into London, arriving at Victoria station at approximately 5.40pm Metropolitan Police Police release images of suspects in connection with Salisbury attack CCTV – Salisbury train station, 11:48hrs on 4 March 2018 They then travelled on London public transport to Waterloo station and were in the area between approximately 6pm and 7pm. They travelled to the City Stay Hotel in Bow Road, East London, where they stayed on Friday, 2 March, and Saturday, 3 March. On Saturday, 3 March, they left the hotel and took the underground to Waterloo station, arriving at approximately 11.45am, where they caught a train to Salisbury, arriving at approximately 2.25pm Metropolitan Police Police release images of suspects in connection with Salisbury attack City Stay Hotel in Bow Road Police officers stand outside the City Stay Hotel in Bow where on Sunday, 4 March, 'Boshirov' and 'Petrov' made the same journey from the hotel as they did the previous day, again using the underground from Bow to Waterloo station at approximately 8.05am, before continuing their journey by train to Salisbury Getty Police release images of suspects in connection with Salisbury attack CCTV – Wilton Road, Salisbury, 11:58hrs on 4 March 2018 CCTV shows them in the vicinity of Mr Skripal’s house and we believe that they contaminated the front door with Novichok Metropolitan Police Police release images of suspects in connection with Salisbury attack CCTV – Fisherton Road CCTV image of both suspects on Fisherton Road, Salisbury at 13:05hrs on 4 March, 2018 Metropolitan Police Police release images of suspects in connection with Salisbury attack CCTV – Salisbury train station, 13:50hrs on 4 March 2018 They left Salisbury and returned to Waterloo Station, arriving at approximately 4.45pm and boarded the London Underground at approximately 6.30pm to London Heathrow Airport Metropolitan Police Police release images of suspects in connection with Salisbury attack CCTV – Heathrow airport security, 19:28hrs on 4 March 2018 From Heathrow Airport, they returned to Moscow on Aeroflot flight SU2585, departing at 10.30pm Metropolitan Police/PA Police release images of suspects in connection with Salisbury attack Scene investigations The police investigation was carried out over 6 months. Ex-Russian spy Sergei Skripal and his daughter Yulia were found on March 4 in a critical condition on a bench outside the Maltings shopping centre in Salisbury AFP Police release images of suspects in connection with Salisbury attack Victims Former Russian spy Sergei Skripal, right, and his daughter Yulia Rex Police release images of suspects in connection with Salisbury attack Victims Detective Sergeant Nick Bailey who rushed to the aid of the Skripals was also taken to hospital in a serious condition after falling ill when attempting to help them PA Police release images of suspects in connection with Salisbury attack Victims Dawn Sturgess, a 44-year-old mother of three, died after falling ill when partner Charlie Rowley gave her a perfume bottle that contained the nerve agent Novichok Facebook/AFP/Getty Police release images of suspects in connection with Salisbury attack Scene investigations The home of Charlie Rowley in Muggleton Road, Amesbury, where he and Dawn Sturgess were exposed to the deadly nerve agent Novichok PA

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 – his phone later 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 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.

'Nothing criminal' about UK Skripal suspects says Putin

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.