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The agent - codenamed Apollo - was recruited in a spectacular coup by Britain’s Secret Intelligence Service in Rome, just weeks after the Novichok nerve-agent attacks in Salisbury. While he held a position in Russia’s embassy, his real task was to harvest sensitive and classified information about Nato from staff working within the department of former defence minister Roberta Pinotti. Sources say he had been groomed for several months by an MI6 agent posing as an art dealer, after expressing a desire to leave Moscow because of his opinion that Russian president Vladimir Putin is “determined to march towards conflict with the West.” Last night intelligence sources revealed that ‘Apollo’ was brought to Britain in April and debriefed “for several weeks” at a rural safe-house.

As part of that debrief, he was able to provide both MI6 and MI5 wth a “wide spectrum of routine and sensitive information about how Moscow operates its network of spies across the world”. He was then shown CCTV images of Alexander Petrov and Ruslan Boshirov, the aliases used by two GRU agents sought by New Scotland Yard on attempted murder changes. “He was able to identify these men as GRU operatives, which corroborated our own information,” added the source. Crucially, he also provided their true identities.

Alexander Petrov and Ruslan Boshirov are being sought on attempted murder charges

Though sources would not specify what role 'Apollo' occupied at the embassy, it is likely that he was a GRU field agent operating in the same manner as the 23 expelled from Russia’s London embassy in March. The US expelled more than 60 Russian spies as part of the show of international solidarity by 20 countries following the brazen attacks. Rome expelled just two. Other sources have told how the fake Nina Ricci fragrance bottle used to carry the deadly nerve agent had been especially engineered to the highest standards in Russia and included a non-return valve. In a briefing last week Assistant Commissioner Neil Basu, National Lead for Counter Terrorism Policing, said: “The manner in which the bottle and packaging has been adapted makes it a perfect cover for smuggling the weapon into the country, and a perfect delivery method for the attack against the Skripal’s front door.” In any case, Novichok is designed not to be detected by standard airport equipment.

According to intelligence sources, MI6 used a Russian agent to help identify the Salisbury attackers

But the Russian agent revealed that it was ‘highly unlikely” that either Petrov and Boshirov would have personally carried the perfume bottle during the Aeroflot flight from Moscow to Gatwick on March 4. Under normal protocols, he said, that job would have been passed to a middle man, who would have deposited the vial in a “Dubok”, the Russian word for a Dead Letter Box - an agreed location where communications, documents, or equipment is covertly placed for another person to collect without direct contact between parties. “What we were told is that they arrived in London as clean skins and picked up the nerve agent from a DLB which, he said, was in London. “Then the two agents took it back to their hotel to prepare for their mission - where the Prime Minister revealed traces of Novichok was found.”

Former Defence Minister Roberta Pinotti

The MI6 source added; “It’s both easy and perhaps understandable for members of the public to look at what occurred in Salisbury and regard it as a British intelligence failure. But we are doing good work.” While Britain’s intelligence services learned of Petrov and Boshirov in the early stages of the investigation, the decision was made to delay making this knowledge public until last week. Partly, this was to give time for 250 detectives from across the Counter Terrorism Policing Network to build their case. But it was also part of a wait-and-see game following the launching of a Europe-wide operation to seize and arrest the pair. While Assistant Commissioner Basu confirmed that Patrov and Boshirov had used their aliases before, the extent to which they had carefully nurtured their cover identities before their actions in Salisbury was laid bare last night.

The Russian embassy in Rome