The move triggered instant diplomatic repercussions, as Britain summoned the Russian ambassador and told him it expected full cooperation over the case, but a Moscow judicial source ruled out handing over the suspect, Andrei Lugovoy.
''Russia should comply with our legal request,'' Prime Minister Tony Blair's official spokesman said.
He stressed that while Britain had important political and economic ties with Russia: ''This doesn't in any way obviate the need for the international rule of law to be respected and we will not in any way shy away from trying to ensure that happens in a case such as this.'' A source at the Russian prosecutor-general's office told RIA Novosti news agency: ''Under the constitution of the Russian Federation, Russian citizens cannot be handed over to foreign countries for prosecution and Lugovoy appears to be a Russian citizen.'' The murkiest case of murder and espionage since the Cold War has already strained relations between the two countries, and the extradition move looked set to aggravate tensions further.
''I have today concluded that the evidence sent to us by the police is sufficient to charge Andrei Lugovoy with the murder of Alexander Litvinenko by deliberate poisoning,'' said Ken Macdonald, head of the Crown Prosecution Service (CPS).
Litvinenko, a former KGB agent who had become a fierce Kremlin critic in exile, met Lugovoy and another Russian businessman, Dmitry Kovtun, at the Pine Bar of London's Millennium Hotel on November 1 last year.
Within hours, he had fallen seriously ill. He suffered an agonising death over the next three weeks as his organs gradually failed. Litvinenko died in a London hospital on November 23 and doctors diagnosed polonium poisoning.
DEATHBED LETTER In a letter dictated on his deathbed, Litvinenko, who had acquired British citizenship weeks before he was poisoned, accused the Kremlin and Russian President Vladimir Putin of his murder.
Moscow dismissed the accusation as ridiculous. It has launched its own investigation into Litvinenko's death and denies that its security services played any part.
Lugovoy, a former KGB bodyguard who later worked as head of security for tycoon Boris Berezovsky, has previously laughed off reports Britain would seek his extradition.
He has denied killing Litvinenko and lashed out at British media for demonising him.
Macdonald said prosecuting Lugovoy would clearly be in the public interest.
''In those circumstances, I have instructed CPS lawyers to take immediate steps to seek the early extradition of Andrei Lugovoy from Russia to the United Kingdom, so that he may be charged with murder - and be brought swiftly before a court in London to be prosecuted for this extraordinarily grave crime,'' he said.
A spokeswoman for the CPS said it would ask the police to obtain an arrest warrant, which would then be sent by the interior ministry to Russian authorities.
''The ball is now in the Russians' court,'' she said. ''We can't speculate on what the Russians will do.'' REUTERS DS KP1656