Britain and Russia are conspiring to shut down the inquest into the death of Russian spy Alexander Litvinenko to preserve trade interests, a lawyer for his widow has suggested.
Foreign Secretary William Hague has moved to exclude details of the former KGB agent's ties to MI6 from the inquiry saying they could pose a "risk of serious harm to the public."
But Ben Emmerson QC, representing Mr Litvinenko's widow Marina suggested attempts to withhold evidence from the pre-inquest review pointed towards a conspiracy at the highest levels of government.
The inquest was due to formally open on May 1, more than six years after Mr Litvinenko, 43, was poisoned with polonium-210 while drinking tea, allegedly at a meeting with two Russians - former KGB contacts Andrei Lugovoy and Dmitry Kovtun - at the Millennium Hotel in London's Grosvenor Square.
Prosecutors named Lugovoi as the main suspect in the case following Mr Litvinenko's high profile death in November 2006.
Earlier, Coroner Sir Robert Owen hinted that the inquest was unlikely to open, as scheduled, on May 1, owing to the complexity of the investigation which must conclude first.
Mrs Litvinenko has expressed dismay as it emerged her late husband's inquest was likely to be further delayed, amid concerns it could be shelved.
The pre-inquest review, at London's Royal Courts of Justice, was told Mr Hague had signed a public interest immunity (PII) certificate to prevent certain details relating to the case from being placed in open court for security reasons.
The nature of this evidence has not been revealed.
Mr Emmerson said such a move suggested the British government was acting to protect relations with Russia.
"The British government, like the Russian government, is conspiring to get this inquest closed down in exchange for substantial trade interests which we know Mr Cameron is pursuing," he said.
Referring to images of Russian president Vladimir Putin and Prime Minister David Cameron seen together at the Olympics in the summer, he added: "One has to ask what is going on at the highest level of Her Majesty's Government, particularly when the highest levels are building bridges with the Kremlin."
And he called on the government to provide more detail relating to the information it wanted to withhold, to avoid the "frightening prospect" of proceedings being "suborned to the Russian Federation".
He added: "We cannot allow Her Majesty's Government, by misusing the PII system, to use this inquest to dance to the Russian tarantella."
He told the hearing: "This has all the hallmarks of a situation which is shaping up to be a stain on British justice", adding: "The British government's position is untenable."
Mr Emmerson said Mrs Litvinenko, who listened intently throughout proceedings, was "extremely disappointed" by the possible setback and warned the coroner he should not allow the process to be "bogged down" by the "government's attempt to keep a lid on the truth".
He added: "We know nothing about why these applications are being made and we are dancing in the dark."
The pre-inquest review also heard applications from oligarch Boris Berezovsky and various media outlets pushing for evidence to be placed in the public domain.
At a previous hearing, it emerged evidence found by the government showed the Russian state was involved in Mr Litvinenko's murder.
The former Russian agent was revealed to have been hired by MI6 for a number of years and was working with the Spanish secret service investigating the Russian mafia shortly before his death.
He was said to regularly meet with an MI6 handler, named only as Martin, in central London and was paid by both the British and Spanish secret services into a joint bank account he held with his wife.
Prosecutors named Lugovoi as the main suspect in the case but Russia has refused to extradite him to the UK for questioning.
Today's proceedings - which also addressed Britain's apparent failure to provide Mrs Litvinenko with legal funding - were adjourned until tomorrow when Sir Robert is expected to announce whether the Government should be required to shed light on the nature of the evidence that it aims to conceal.