By Peter Griffiths
LONDON (Reuters) - Britain's long-delayed inquest into the death by radioactive poisoning of Russian spy Alexander Litvinenko could be abandoned after the coroner partly upheld a British government request to withhold crucial evidence.
Robert Owen, a senior judge acting as coroner, said on Friday keeping some of the evidence secret would make it impossible to hold a "full, fair and fearless inquiry" into the death of the vocal critic of Russian leader Vladimir Putin.
Litvinenko, 43, died after drinking polonium-210, a radioactive isotope, that had been slipped into his tea at a London hotel in 2006. In a deathbed statement, he accused Putin of ordering his murder, a claim Russia has denied.
His death plunged relations between London and Moscow to a post-Cold War low, although British Prime Minister David Cameron visited Russia this month as part of efforts to improve ties.
In a written ruling, the coroner partially upheld a request by British Foreign Secretary William Hague to withhold evidence relating to the possible involvement of the Russian state in Litvinenko's death and whether it could have been prevented.
The coroner also agreed to keep secret information that could undermine trust in the British government or "cause real harm to the UK's international relations".
Without being able to assess all the evidence in open hearings, Owen said he would be unable to "discharge my duty to undertake a full, fair and fearless inquiry into the circumstances".
"The inquiry would be incomplete and a verdict potentially misleading and/or unfair," he wrote in the ruling, which was partly censored for security reasons.
Those involved have two weeks to respond and a further hearing is due on June 11 when the coroner will announce what happens next. A British government spokesman said: "The government will carefully consider this judgment."
The British authorities could now order a form of inquiry that would allow evidence to be heard in secret instead of an inquest, a hearing held under British law to determine the cause of death when a person dies unexpectedly.
Litvinenko's widow Maria said she was "utterly dismayed" by the ruling, which she described as a political fix to help Russia and Britain rebuild their relations.
"All those concerned with exposing the truth will be shocked and saddened that a political deal has been done between the two governments to prevent the truth from ever seeing the light of day," she said in a statement.
At a pre-inquest hearing in February, the Litvinenko family's lawyers said Britain was trying to cover up his work for its Secret Intelligence Service, known as MI6, and material showing Russia was behind his death.
Russian Foreign Ministry spokesman Alexander Lukashevich said in December that the claims were unfounded and Moscow hoped that an investigation would show them to be so.
(Editing by Robin Pomeroy)