Britain is seeking to withhold information about Russian dissident Alexander Litvinenko at the forthcoming inquest into his death to avoid damage to trade deals with Moscow, a court was told on Tuesday.
A pre-inquest hearing at the Royal Courts of Justice heard that Foreign Secretary William Hague had signed a public interest immunity (PII) certificate to prevent evidence relating to the case being placed in the public domain.
This was because disclosure risked "serious harm to the public interest", Hague wrote in the document which has been made public.
But almost a dozen media organisations including the BBC and the Guardian newspaper are challenging the certificate, as is Litvinenko's widow Marina.
Ben Emmerson, a lawyer for Marina Litvinenko, told Tuesday's hearing that Britain was trying to shut down the inquest as it sought to improve ties with Russia, which were severely strained over the 2006 killing of Litvinenko.
"The British government, like the Russian government, is conspiring to get this inquest closed down in exchange for substantial trade interests which we know (Prime Minister) Mr (David) Cameron is pursuing," Emmerson said.
He added: "This has all the hallmarks of a situation which is shaping up to be a stain on British justice."
The inquest is expected to examine the Russian state's alleged involvement in Litvinenko's death -- which it denies -- as well as that of the British state in failing to protect the dissident, who was also a British citizen.
Emmerson told a previous hearing in December that Litvinenko was actively working for British spy agency MI6 at the time of his agonising death from highly radioactive Polonium-210 in November 2006.
Litvinenko had also worked for the Spanish security services at MI6's request, providing information on the activities of the Russian mafia, he said.
Coroner Robert Owen is expected to give his decision on the PII on Wednesday.
The inquest, a fact-finding inquiry designed to establish the circumstances surrounding Litvinenko's death, was due to start in May but Owen warned that the complex issues involved could see it delayed further.
British police have identified Andrei Lugovoi, a former FSB agent, as the main suspect in Litvinenko's death, but Moscow has refused to extradite him.