The poisoned spy lying in a critical condition in hospital was codenamed ‘Forthwith’ and provided MI6 with a host of revealing information on Russian agents.
Sergei Skripal, who was ‘deliberately targeted’ in a nerve agent attack along with his daughter in Salisbury on Sunday, was regarded as a ‘highly valued spy’ for MI6.
It is also reported that Mr Skripal was ‘useful’ to foreign intelligence services after he was returned to Britain in a spy swap in 2010.
Mr Skripal, 66, provided a wealth of intelligence on the GRU – Russia’s foreign intelligence service – over a ten-year period, according to The Times.
Sergei Skripal (left, in 2006 and, right, during his time in the Russian military) is fighting for his life after being exposed to an unknown substance. He had been brought to Britain in a spy swap in 2010 after he was caught passing Russian secrets to MI6. But a documentary claimed that he had in fact begged not to be swapped.
A police tent has been put up over the park bench where Skripal and his daughter appeared ‘catatonic’
One security officer told the Financial Times: ‘There was interest from friendly foreign services after he was released in the spy swap.
‘He was useful for a limited period.’
Among the trove of data supplied to British authorities was the GRU’s entire telephone directory.
He was first identified as a potential recruit for the Spanish intelligence – but run by British intelligence because it was believe he would respond better to British handling.
While station in Spain as a GRU officer, Mr Skripal was approached by an MI6 officer who posed as a Spanish business partner, according to intelligence sources.
The first meeting between the Russian and British intelligence agents took place in 1996 when he was 44.
After he was diagnosed with diabetes he returned to Moscow, but frequently returned to Spain to recuperate.
His contact with MI6 would gradually expand to the point where he was appointed his own full-time case officer.
Emergency services found Sergei Skripal and a woman, said to be his daughter Yulia, slumped over a bench at The Maltings shopping centre before they were transported to Salisbury District Hospital, where a major incident was declared on Monday
Mr Skripal was among of a group of top spies exchanged in Vienna in 2010 (left) for a group of Russian agents including the glamorous Anna Chapman (right)
Mr Skripal retired from the GRU in 2000 but managed to secure a job through a former army colleague in the Moscow provincial government – continuing to provide MI6 with intelligence.
He was even bought a timeshare holiday home near Malaga, where he would meet the case officer over periods of three days.
Following each session, Mr Skripol would be paid between $5,000 and $6,000 in cash, which he then deposited into a Spanish bank account.
Sources also revealed that while his initial motivation was financial, he became increasingly more interested in Britain.
But MI6 made sure not to bring him to Britain in order to avoid giving away any link between ‘Forthwith’ and the service.
In one instance, Mr Skripol was said to have called an emergency meeting in Spain, during which he demanded $10,000 in cash and an MI6 officer flew out with the money the next day.
Intelligence sources believe Russia could be targeting double agents living in Britain due to MI6’s success in recruiting spies since the collapse of the Soviet Union.
At least a dozen former MI6 agents are thought to be living in the UK under varying degrees of protection.
Their names are kept secret but their identities are not necessarily unknown to President Putin, himself a former Lieutenant Colonel in the KGB.
It is understood that Mr Skripol did not expose a large number of Russian spies working undercover in the West.
But he was able to provide specific information on Russian military intelligence structure, including the identities of hundreds of officers.
The intelligence he gathered was also shared with MI5 and other allies, including the CIA.
Even in his retirement from the GRU, he would maintain contact with British intelligence before finally being exposed as a double agent and arrested in 2004.
He was jailed for 13 years in 2006 and was only released in the high-profile spy-swap which involved glamourous Russian agent Anna Chapman, who had been caught spying in the US
Once married to a British former public schoolboy, the seductive spy is now a propagandist for the Kremlin
MI6 first learnt that ‘Forthwith’ had been compromised when he failed to attend a meeting that same year.
He was jailed for 13 years in 2006 and was only released in the high-profile spy-swap which involved glamourous Russian agent Anna Chapman, who had been caught spying in the US.
After being debriefed by British security services, he was given a new life living in a £340,000 house in Wiltshire.
At the time of his arrest he was mocked as ‘the spy with the Louis Vuitton bag’ after grainy pictures showed him with an expensive looking bag at an airport en route on one meeting with his handlers.