RUSSIAN officials announced yesterday that a criminal investigation had been opened into allegations by a former tax police officer that he was recruited as an informant by MI6 with the help of Alexander Litvinenko, the former KGB agent who died of polonium poisoning in London last year.

Vyacheslav Zharko is said to have turned himself in to the FSB, the successor to the KGB, 10 days ago and confessed to having worked for British intelligence since 2002. He claims that he was introduced to MI6 officers by Litvinenko during a trip to London in that year.

Zharko said he met his British handlers regularly in Turkey, Finland and Cyprus and supplied them with analytical reports on Russia's economy and politics. In return, he claims, he was paid about £60,000. He estimates that MI6 spent an additional £150,000 on expenses.

"I needed money so when Litvinenko told me that I could earn easy cash by collaborating with British intelligence I agreed," Zharko, 36, told The Sunday Times in his first interview with a western newspaper. "I saw myself as a consultant. I began to worry after Litvinenko's death because I feared I'd be sucked into something too dangerous. That's when I turned myself in."

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The FSB, which has investigated Zharko, backs his claims but will not prosecute him for espionage, saying that he did not reveal any state secrets and had come forward voluntarily. His testimony comes a month after Andrei Lugovoi, a former KGB officer named by the Crown Prosecution Service as the prime suspect in the death of Litvinenko, accused MI6 of trying to recruit him.

Russia has refused to extradite Lugovoi, who met Litvinenko on the day he was poisoned, to face trial in Britain and the Kremlin has angrily rejected accusations that it was behind the murder. Like Zharko, Lugovoi, who has protested his innocence, claims British intelligence sought to recruit him with Litvinenko's help.

The fallout over Litvinenko's death, which also left dozens of people contaminated with polonium 210, together with the subsequent row over Lugovoi, has plunged relations between Britain and Russia to their lowest point since the end of the cold war.

The dispute has also provoked a propaganda battle between MI6 and the FSB, two former foes that, officially at least, are partners in the fight on terrorism. British investigators are believed to suspect that Litvinenko, a former FSB officer who fled to Britain and was granted asylum, and who became a fierce critic of Vladimir Putin, the Russian president, was killed by his former employer.

The FSB rejects the claim and is now hitting back, using Zharko's testimony to highlight allegations of secret MI6 operations in Russia. "For months we've been accused of killing Litvinenko," said an FSB source.

"The Brits have been waging an information war against us and now we are responding in kind. We have gone public with Zharko's story because it proves that Britain is actively spying against Russia and that Litvinenko was in cahoots with MI6." Zharko claimed he had first met Litvinenko through Boris Berezovsky, the exiled Russian tycoon and opponent of Putin.

Berezovsky has been granted asylum in Britain. A former tax police officer in St Petersburg, Zharko had turned to Berezovsky for help in 2000 when an investigation he had led into a rival tycoon was threatened for political reasons. According to Zharko, Berezovsky — who at the time had fallen out with the tycoon under investigation — used his influence to keep the investigation open.

In 2002 Zharko left the tax police but stayed in touch with Berezovsky who by then had fled to Britain after falling out with Putin. It was during a trip to London five years ago that the billionaire, who according to Zharko knew him under the false name of Vladislav Petrov, put him in touch with Litvinenko. In turn, Litvinenko introduced Zharko to several British "friends", who claimed to be business consultants but who later revealed themselves as MI6 officers and told him they were interested in recruiting him as an informant.

"They agreed to pay me €2,000 [£1,355] a month," Zharko said. "I was told I shouldn't travel to London any more because Berezovsky's entourage was closely watched by Russian intelligence. I was supplied with a mobile phone I was to use to make contact with them, but only outside Russia.

"Litvinenko led them to believe that I'd worked in Russian intelligence so they thought I was a good catch." According to Zharko, during his years of secret work for MI6 he had several meetings in the West with a total of four undercover British handlers. He talked fondly about one of the MI6 agents.

"We spent many nights drinking together and he once told me how he had photographed some secret documents in the toilets of a Moscow restaurant," he said.

Zharko said that at first his British handlers had been interested in information on several Russian companies. Then they asked him to compile a series of analytical reports on the political situation in Ukraine in the run-up to the country's Orange revolution and were also interested in information on any FSB operations against western non-governmental organisations working in Russia.

Zharko claims he supplied his case officers with information he compiled only from open sources. His final meeting with his handlers took place last November in Istanbul, a few days after Litvinenko's death, he said. He last spoke to them on the phone in June.

It is not the first time the FSB has publicly claimed to have exposed an MI6 operation. Last year it leaked footage of four diplomats posted at the embassy, allegedly downloading secret data from a transmitter concealed in a fake rock left in a Moscow park.

Relations between the two countries have been steadily worsening since. For months members of a pro-Kremlin youth group harassed Sir Anthony Brenton, the British ambassador in Moscow, after he attended an opposition gathering. Last week Brenton issued an angry public denial after a Russian paper claimed that asylum could be bought in Britain.

"We are in the middle of an information battle," said a British diplomat who was based in Moscow. "Relations were hard enough before the Litvinenko case. They've since taken a sharp turn for the worst. Expect more salvos to be fired."

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