Alexander Litvinenko in hospital
Lugovoi profile
Sir Ken Macdonald said Andrei Lugovoi should be tried for the "grave crime".
Mr Litvinenko, 43, an ex-FSB agent and a critic of Russian President Vladimir Putin, died in London last November.
Mr Lugovoi denied any involvement and said the charges against him were "politically motivated"; the Kremlin said he would not be extradited.
Mr Lugovoi met Mr Litvinenko on the day he was taken ill.
Radioactive isotope polonium-210 - the substance found in Mr Litvinenko's body - has been detected in a string of places Mr Lugovoi had visited in London.
But Mr Lugovoi has insisted he was a witness and a victim but not a suspect.
'Well-founded distrust'
"I consider that this decision to be political, I did not kill Litvinenko, I have no relation to his death and I can only express well-founded distrust for the so-called basis of proof collected by British judicial officials," Russian news agencies quoted Mr Lugovoi as saying.
The formal submission of a request for Mr Lugovoi's extradition is expected to take place before the end of the week, after it has been translated.
A spokesman for the Kremlin said Russia's constitution did not allow its nationals to be extradited.
Andrei Lugovoi has strongly denied involvement
Profile of accused
The spokesman added it was waiting for the "British side to actually do something rather than make statements".
The Russian general prosecution service also said there was "no way" Mr Lugovoi could be extradited because of constitutional constraints.
But the service's spokesman added that a Russian citizen who had committed a crime in another country "should be prosecuted in Russia with evidence provided by the foreign state".
UK Foreign Secretary Margaret Beckett said she had told the Russian ambassador that she expected "full co-operation" with regards extraditing Mr Lugovoi.
And Prime Minister Tony Blair's official spokesman said people should wait and see what Russia's "considered legal response" was to the extradition request.
He pointed out that in 2001 Russia had signed the 1957 EU convention on extradition.
Mr Litvinenko, who was granted political asylum in the UK in 2000 after leaving Russia and went on to take British citizenship, died at University College Hospital on 23 November.
I have instructed CPS lawyers to take immediate steps to seek the early extradition of Andrei Lugovoi from Russia
Sir Ken Macdonald
CPS statement on Litvinenko
Sir Ken Macdonald told a news conference: "I have today concluded that the evidence sent to us by the police is sufficient to charge Andrei Lugovoi with the murder of Mr Litvinenko by deliberate poisoning.
"I have further concluded that a prosecution of this case 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 Lugovoi 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."
International investigation
Mr Litvinenko's widow Marina said that she welcomed the decision on what was a "big day" for her.
She said: "I am now very anxious to see that justice is really done and that Mr Lugovoi is extradited and brought to trial in a UK court."
A period of tense relations between Britain and Russia is expected
Paul Reynolds
World affairs correspondent, BBC News website
'Stand-off' over spy case
She added that any court case should be held in Britain, and that she believed more than one person was responsible for her husband's death.
The counter-terrorism command of the Metropolitan Police has been conducting a detailed international investigation into Mr Litvinenko's death. The police inquiry, during which officers followed a trail of polonium radioactivity at a series of locations visited by Mr Litvinenko in London before he died, eventually took them to Moscow.
His friends, including London-based Russian tycoon Boris Berezovsky, have accused the Kremlin of ordering his assassination but the Russian government has rejected such claims.
Police passed a file to the Crown Prosecution Service in January.
__NOTOC__
The United Kingdom  has announced that it has sufficient evidence that a former FSB (formerly ) officer should be charged with the murder last year of Alexander Litvinenko.

 is charged with the murder of Mr Litvinenko, by the administration of the highly radioactive  in a hotel in Mayfair, London, on 1st November 2006. Mr Litvinenko, 43, died of radiation sickness in University College Hospital on 23rd November. The case received considerable publicity at the time, with pictures of Litvinenko in hospital and showing the effects of the radiation poisoning. 

Litvinenko was himself a former Russian FSB agent and was a critic of Russian President Vladimir Putin. He had tried to publish a book in Russia describing Putin's rise to power as having been organised by the KGB. He was forced to flee from Russia and had lived for some time in London, being granted British citizenship in October 2006.

He continued his dissent throughout the remainder of his life, culminating in a posthumous  published on 24th November 2006 alleging that Putin was responsible for his death.

===Investigation and charge===


Litvinenko's murder led to a lengthy investigation by the  and additional specialist police forces following a trail of sites which had been contaminated with radiation, leading eventually to Moscow. A file of evidence was sent in January 2007 to the Crown Prosecution Service for consideration as to whether any criminal charges might be brought.

The Director of Public Prosecutions, Sir Ken Macdonald, QC, in announcing the decision to prosecute, said: "Prosecutors from CPS Counter Terrorism Division have carefully considered the material contained in that police file. They have also asked the police to carry out further inquiries, which are now complete. And, finally, they have consulted with me."

"I have today concluded that the evidence sent to us by the police is sufficient to charge Andrey Lugovoy with the murder of Mr Litvinenko by deliberate poisoning. I have further concluded that a prosecution of this case 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 Andrey 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."

===Extradition unlikely===

The announcement followed the summoning of the Russian Ambassador to London to the Foreign Office to be told by Foreign Secretary  that she expected that the Russian authorities would co-operate fully with Britain to arrange the extradition of Mr Lugovoi to stand trial in London. However there are indications from Moscow that the extradition of Lugovoi, who denies any involvement in the murder, is unlikely to happen. Marina Gridneva, spokeswoman for the Russian Prosecutor General's Office said that "under Russian law, a citizen of the Russian Federation cannot be handed over to a foreign country".

There is no bilateral extradition treaty between Russia and the UK. Legislation passed by Russia to deal with individual requests from countries in Europe rules out the extradition of its citizens, even to the extent that when in 1966 it became a signatory to the European convention on extradition, it granted itself an exemption from such a course.

However it has been reported that such a ban on extradition would not necessarily prevent Lugovoi being tried in Russia using evidence from the UK.