Until the British “rock” was exposed this week, the Federal Security Service, the KGB’s successor agency, had not had many new toys for its collection of Cold War spy gadgets — including glasses with suicide poison in the frames and a radio receiver disguised as a tree. However, if intelligence experts are correct, it can expect more trophies as Western spy agencies step up their operations in Russia to a level not seen since the Soviet collapse.

Western intelligence services said last year that Russia had aggressively escalated its spying on their patches since President Putin — a former KGB spy — took power in 2000.

It is now considered second only to China in terms of how aggressively it is seeking Western technological, commercial and military secrets.

What is less widely publicised is that US and British intelligence have also been actively recruiting Russian-speaking agents in tandem with Russia’s growing economic and political clout, intelligence experts say.

“The Cold War has ended; now we have the hot peace,” Oleg Nechiporenko, a prominent former KGB spy, told The Times. Once called “the best KGB agent in Latin America” by the CIA, he was thrown out of Mexico in 1971 for plotting to overthrow the government.

He said that he was not surprised by the FSB’s allegation that it had caught four British Embassy employees spying. “These days, you see leaders hugging and smiling, but everyone still has their own geopolitical interests — that’s where the special services come in,” he said.

John Scarlett, the MI6 chief, is also no stranger to the rivalry between British and Russian spooks. He was expelled from Moscow in 1994 after being exposed as the MI6 desk officer at the British Embassy.

The FSB offered no definitive figures for the number of Western spies operating in Russia. but Nikolai Patrushev, the FSB chief, has said that his agents caught 26 foreign intelligence officers and 67 of their agents in 2005. The FSB apprehended 18 foreign spies in 2004 and 13 in 2003. “Reconnaissance is not only not waning,” Mr Patrushev said in November, “it is strengthening.”

In the past two years the West has again started to see Russia as a security threat, as President Putin re-asserts the Kremlin’s authority at home and in the former Soviet Union. Russia is sitting on a vast nuclear arsenal as well as poorly guarded stockpiles of nuclear material. It has close ties to governments deemed hostile to the West, particularly Iran, Syria and North Korea; and it sells billions of dollars of weaponry to China every year.

Perhaps most importantly, the West is becoming increasingly dependent on Russian energy. “An informant within Gazprom would be priceless,” said one Moscow-based diplomat, referring to the Russian gas monopoly.

Western intelligence agencies are also having to channel ever more resources into combating Russian agents. A British security source said: “The UK is a high-priority espionage target and of greatest concern are the Russians and Chinese.”

Sergey Lebedev, the director of the Russian Foreign Intelligence Service, denies an escalation of operations in the West. “Russian intelligence has reduced its presence overseas and substantially restructured its activities,” he said last month.

Oleg Gordievsky, a former KGB officer who was a double agent, said, though, that 34 Russians at the Russian Embassy and various international organisations in Britain were spies. The security services were unable to confirm the figure, but Mr Gordievsky, who has lived in Britain since his defection in 1985, keeps close ties with MI6 and MI5. “I know the figure is accurate,” he said.

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