Two women who were part of a Russian spy network run from the UK are named for the first time today by a BBC investigation.

Bulgarian nationals Cvetelina Gencheva and Tsvetanka Doncheva took part in elaborate surveillance operations against people spied on by the cell.

Neither woman answered questions when contacted by the BBC.

Ms Gencheva, an airport worker, hung up when contacted by phone, and said she did not want to comment on the case in response to a subsequent letter.

Ms Doncheva denied being herself and walked away when approached near her home in Vienna, Austria.

Six other Bulgarians are awaiting sentencing in London for their roles in spying for Russia as part of the cell.

Police described the network as a “highly sophisticated” operation that threatened lives. Three pleaded guilty, admitting knowing they were working for Russia, while three more were convicted this month after a trial at the Old Bailey having failed to persuade the jury that they didn’t.

The cell was directed from abroad by Jan Marsalek, originally from Austria, who was a business executive in Germany who became a Russian intelligence asset. The cell’s targets included journalists who have investigated Russian espionage. One, Roman Dobrokhotov, told the BBC he believed Vladimir Putin was ultimately responsible.

The court heard about two mystery women who took part in surveillance operations in Europe.

The BBC tracked down and confirmed the identities of both women through open source digital research and speaking to sources.

Ms Gencheva, who lives in the Bulgarian capital Sofia, exploited her work in the airline industry to obtain private flight details of people targeted by the cell.

Spies followed the people onto planes and were booked in nearby seats, getting so close as to see what was being typed into their targets’ mobiles phones, even at one stage identifying a Pin number for a phone belonging to journalist Roman Dobrokhotov.

Ms Gencheva was part of a team sent to Berlin to spy on Mr Dobrokhotov, and she was a member of chat groups with three of those convicted of spying in the UK case – cell leader Orlin Roussev, Biser Dzhambazov and Katrin Ivanova – which were used to co-ordinate the spying.

She provided flight details for journalist Christo Grozev, and was tasked with gathering as much travel information as possible on another target of the cell, Russian dissident Kirill Kachur.

During the Old Bailey trial, the mystery airline worker was known as “Cvetka” or “Sveti”.

The BBC first identified Ms Gencheva through her social media profiles. On Facebook, she had interacted with Katrin Ivanova and Biser Dzhambazov.

We then found she was an airline worker.

According to her Linkedin profile, she has held positions in ticket sales for travel companies. Bulgarian company filings say she is the sole owner of International Aviation Consult.

Screen captures of travel data found on a hard drive belonging to cell leader Roussev were from airline industry software known as “Amadeus”.

On her LinkedIn profile, we found Ms Gencheva noted her proficiency with the software.

After the BBC’s research identified Ms Gencheva, a source confirmed to the BBC that she is known to the Bulgarian security services as being connected to the spy network. She is not charged with any offence.

We contacted Ms Gencheva on a Bulgarian phone number she uses for real estate work. She hung up when informed the call was from BBC News and was being recorde