Sergei Skripal: who is the former Russian spy critically ill after ‘substance exposure’ in Salisbury? Throughout the 1990s, Colonel Sergei Skripal led a double life as a Russian intelligence officer by combining his military duties […]

Throughout the 1990s, Colonel Sergei Skripal led a double life as a Russian intelligence officer by combining his military duties with the wholesale passing of Moscow’s secrets to his handlers in MI6.

The precise details of when Mr Skripal began working for the Secret Intelligence Service are unknown but following the collapse of the Soviet Union he was persuaded to begin providing the names of Russian agents operating across Europe to London.

When he was eventually tried in 2006 after retirement, Russian military prosecutors claimed he had been paid $100,000 (equivalent to roughly $180,000 today) for his services.

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Whatever the price of his loyalty, the Russians acknowledged he had caused significant damage to Moscow’s espionage operations. A spokesman for the military court said at the time: “His activities caused a significant blow to Russia’s external security.”

Asset

In Britain, the intelligence supplied by Mr Skripal was highly prized – as an asset he was considered second only to Oleg Gordievsky, the KGB colonel who defected in 1985 and was later decorated in the Queen’s birthday honours.

Even more extraordinary that Mr Skripal’s espionage was the manner of his arrival in Britain.

In 2010, the FBI scored a major coup by uncovering a network of 11 Russian ‘illegals’ sent under deep cover to live as Americans, including the flame-haired Anna Chapman.

In an episode straight from the Cold War, Mr Skripal, who had been serving his jail term in Siberia, and three other Anglo-American spies were exchanged for group. The handover took place at Vienna airport.

Until yesterday, he had faded into obscurity, apparently leading an unremarkable retirement in Wiltshire.