The Guardian reports:

The diplomatic tension between Britain and Russia took a new twist last night when a man linked to the murdered dissident Alexander Litvinenko sought political asylum in Britain. Andrei Sidelnikov, 32, was prevented from leaving Moscow last week by the Russian secret service who intercepted him at the airport but it is understood he arrived in London yesterday from Kiev. Sidelnikov, the leader of a small Russian opposition youth movement, is known to have met Litvinenko in a cafe off Oxford Street on October 30 last year, two days before Litvinenko was poisoned with polonium-210. Sidelnikov was tested for polonium-210 but found not to be contaminated. He said he had no role in Litvinenko's poisoning and offered to assist the Scotland Yard investigation.

Sidelnikov, thought to be close to the exiled billionaire Boris Berezovsky, a leading foe of President Vladimir Putin, said he was making the asylum application because his life was in danger in Russia. Last week, before being barred from leaving Moscow, he claimed he was followed for several days by officers from the FSB, Russia's biggest security agency. He was also questioned about the murder of the journalist Anna Politkovskaya. "I've just landed in London - I'm very happy," he said yesterday. A friend said yesterday he fled to Britain because of "political persecution" by the Russian authorities.

Without citing any evidence, Russian officials have accused Berezovsky of involvement in the Litvinenko case and other murders of Putin opponents. Sidelnikov said he previously travelled to London four times a year, usually meeting Litvinenko. At their final meeting he said Litvinenko told him he was expecting some documents to come from Moscow offering proof of Russian secret service involvement in the Politkovskaya killing. "I understood he was indeed making his own investigation into her death," he said. "He told me he was expecting some papers to arrive to him soon with proof of the FSB involvement. He didn't say who was going to give him such documents."

Last week, Sidelnikov said he was puzzled about why he was questioned over Politkovskaya's death. When he was stopped at a Moscow airport he said he was given a letter from the FSB saying he was not permitted to leave Russia. The Kremlin has refused to extradite to Britain the chief suspect in the Litvinenko murder, Andrei Lugovoi, who is now a Russian MP. Moscow is also angry at Britain's refusal to extradite Berezovsky.