The third Russian agent implicated in the Sailsbury nerve agent attack has been linked to the poisoning of up to three people in Bulgaria.

The existence of a third man was first revealed the The Daily Telegraph. He was identified as a 45-year-old Russian travelling under the alias Sergey Vyacheslavovich Fedotov.

Fedotov, a senior GRU officer who was in the UK at the time of the attempted assassination of Sergei Skripal in March, is believed to have arrived in Bulgaria in 2015 just days before a local entrepreneur and his son became seriously ill after being poisoned with an unidentified substance.

Like the other two suspects, GRU officers Anatoliy Chepiga and Alexander Mishkin, Fedotov's identity was created in 2010, with no prior records of a person with this name ever existing.

It has been revealed by the investigative publication Bellingcat alongside their Russian partners The Insider that on April 24, 2015, Fedotov arrived on a flight from Moscow to Burgan in Bulgaria.

The 45-year-old had been due to board a return flight a week later on April 30 from Sofia to Moscow.

However, he did not show up for the return flight. Instead, late on the evening of April 28, he showed up at Istanbul’s Ataturk airport and bought a last-minute ticket to a flight to Moscow.