The inquest into the death in Britain of Russian dissident Alexander Litvinenko was close to collapse yesterday after the coroner ruled he could not hear evidence about the alleged role of the Kremlin in his poisoning.
Litvinenko's widow Marina said she was "utterly dismayed". She accused Britain of making a deal with Moscow to improve relations chilled by the murder of her husband, who once worked as a spy for Russia.
Coroner Robert Owen announced his decision in a pre-hearing ruling on Friday. It followed an application by Britain's foreign ministry to keep the information concerning Russia secret. But Owen said he would be failing in his duty "to undertake a full, fair and fearless inquiry into the circumstances of Mr Litvinenko's death" if he were forced to disregard the evidence for national-security reasons.
He suggested that the death could instead be considered in a public inquiry in which the evidence alleging Russian state involvement "could be taken into account".
Under English law, evidence cannot be heard in secret as part of an inquest, but could be presented behind closed doors as part of a public inquiry.
The coroner said he now wanted to hear submissions from Marina Litvinenko and the couple's son on the possibility of holding an inquiry, parts of which would have to take place behind closed doors.
Litvinenko, 43, suffered a slow and agonising death after he was poisoned with radioactive polonium-210 slipped into his tea at a London hotel in 2006.
Marina Litvinenko's lawyers said it was a "very sad day for British justice".
Their statement went on: "Mrs Litvinenko is utterly dismayed by the coroner's decision to abandon his search for the truth about Russian state responsibility for her husband's death.
"The effect of today's ruling is to protect those responsible for ordering the murder of a British citizen on the streets of London, and to allow the Russian government to shield behind a claim for secrecy made by William Hague with the backing of the Prime Minister David Cameron."
She said it was a "frightening precedent" for people trying to hold to account the "conspiracy of organised criminals that operate from the Kremlin".
There was no immediate reaction from Russia.
British Foreign Secretary William Hague has sought to prevent information regarding the death from being revealed during the inquest, to start later this year.
The coroner said he partly agreed with Hague's request.
It is thought that Litvinenko, a former agent for Russia's FSB intelligence agency, was working for Britain's Secret Intelligence Service (MI6) at the time of his death and his family believe he was killed on the orders of the Kremlin. British police have sought the arrest of two Russian nationals in relation to the death but Moscow has refused to hand them over. The Litvinenko case plunged relations between Russia and Britain into a deep freeze from which they have only recently emerged.