The British Broadcasting Corporation said it and other news organizations would oppose an effort on Tuesday by the British government to limit information disclosed to the planned inquest into the death of Alexander V. Litvinenko, a former officer in the KGB who died of radiation poisoning in London more than six years ago.
The BBC reported that the government had planned to apply for a so-called Public Interest Immunity certificate, usually issued on the grounds of national security that would prevent the inquest from hearing information on topics which have not been made public.
The authorities’ resistance to full disclosure may force a postponement in the scheduled May 1 start date for the inquest, which would be the first — and likely the only — forum for sworn testimony about the killing, according to a lawyer for Mr. Litvinenko’s widow, Marina Litvinenko.
The lawyer, Ben Emmerson, complained on Tuesday that the preparations for the inquest were becoming “bogged down” by “the government’s attempt to keep a lid on the truth.”
“It is the government’s secret files that are delaying this inquest,” he said, according to the Press Association news agency, which also quoted the coroner, Sir Robert Owen, as saying on Tuesday that “due to the complexity of the investigation which necessarily precedes the hearings” the schedule for the inquest to begin on May 1 “may be a timetable to which it may not be possible to adhere.”
The Guardian newspaper, which is also opposing the government’s effort to restrict evidence, said that it would argue that “the public and media are faced with a situation where a public inquest into a death may have large amounts of highly relevant evidence excluded from consideration by the inquest. Such a prospect is deeply troubling.”
But the Foreign Office said the authorities had made their application in line with their “duty to protect national security and the coroner would rule according to “the overall public interest.”
The case has strained ties between Britain and Russia, reviving memories of the cold war.
Mr. Litvinenko, who styled himself a whistle-blower and foe of the Kremlin, died in November, 2006, weeks after he secured British citizenship. He had fled from Russia to Britain in 2000.
Britain’s Crown Prosecution is seeking the extradition from Russia of Andrei K. Lugovoi, another former KGB officer, to face trial on murder charges. Mr. Lugovoi denies the accusation and Russia says its constitution forbids it from sending its citizens to other countries to face trial.
At a hearing in December in advance of the inquest, which is to start on May 1, Mr. Emmerson, the lawyer representing Marina Litvinenko, said that Mr. Litvinenko was a “registered and paid agent and employee of MI6, with a dedicated handler whose pseudonym was Martin.”
Mr. Litvinenko also worked for the Spanish intelligence service, Mr. Emmerson said, and both the British and Spanish spy agencies made payments into a joint account with his wife. The lawyer added that the inquest should consider whether MI6 failed in its duty to protect him against a “real and immediate risk to life.”
The BBC said Marina Litvinenko would also oppose the British government’s effort to limit information about its knowledge of her husband’s death.
The coroner has said in previous hearings that he will examine what was known about threats to Mr. Litvinenko and would also seek to determine whether the Russian state bore responsibility. In a deathbed statement, Mr. Litvinenko directly blamed President Vladimir V. Putin, who dismissed the accusation.
Russian state prosecutors are expected to be represented at the inquest. Moscow has denied British suggestions that it may have been involved in killing Mr. Litvinenko, who died after ingesting polonium 210 — a rare radioactive isotope — at the Pine Bar of the Millennium Hotel in central London.