The High Court has quashed a decision by the British government not to hold a public inquiry into the murder of former Russian spy Alexander Litvinenko, who died in London in 2006 after being poisoned with a radioactive substance.
Yesterday's judgment means the government will have to reconsider the decision, a diplomatically sensitive one as a public inquiry could delve into the issue of whether Russia was involved in the killing. Moscow denies any involvement.
Litvinenko, 43, died after drinking tea poisoned with a rare radioactive isotope, polonium-210, in a plush hotel. From his deathbed he accused Russian President Vladimir Putin of ordering his murder, a charge the Kremlin has rejected.
The High Court stopped short of calling for an inquiry actually to take place, but said that Home Secretary Theresa May, the interior minister who refused to hold a public inquiry, would have to revisit the issue.
"If she is to maintain her refusal, she will need better reasons than those given in the decision letter," wrote Lord Justice Richards, handing down the unanimous judgment of the three High Court justices who considered the issue.
"The case for setting up an immediate statutory inquiry as requested by the Coroner is plainly a strong one."
Robert Owen, the coroner in charge of the inquest into Litvinenko's death, had requested an inquiry, stating he was not able to address the issue of Russia's alleged involvement. His request was turned down last July.
Lawyers for the former KGB agent's family have argued that Britain wanted to quash any investigation for fear of jeopardising business deals and souring relations with Moscow.
Relations deteriorated to a post-Cold War low after British police and prosecutors said there was enough evidence to charge two former KGB agents, Andrei Lugovoy and Dmitry Kovtun.
Home Secretary May had said she had taken into account the interests of Britain's relations with Russia in deciding not to order a public inquiry, but this had not been the main factor.