Frederico Carvalhão Gil was given €10,000 and a bottle of whisky in exchange for a memory stick loaded with Nato secrets

Italy has handed a suspected Russian spy back to Moscow two months after he was allegedly caught buying Nato secrets from a Portuguese agent.

European security sources said that the detention of Sergei Pozdnyakov would have embarrassed and enraged Moscow at a time of tension between Russia and the West. “This was a counter-intelligence coup for the Italians and the Portuguese,” one source said.

Court documents suggest that the Russian had already got his hands on Nato secrets from the same alleged agent.

Mr Pozdnyakov, suspected of being a senior member of Russia’s Foreign Intelligence Service, had allegedly travelled to Italy without obtaining diplomatic immunity — a basic error of tradecraft.

Paying an official for secret information is illegal, although unspoken diplomatic rules usually mean