Britain Cites Grave Risks in Leaked Data It Seized LONDON - A standoff between the British government and The Guardian over national security and press freedom entered its latest round on Friday when the high court extended police powers to analyze encrypted material seized from the partner of one of the newspaper's journalists this month. The decision, which slightly expanded the authority of the police to investigate the digital files, came after a senior national security adviser to Prime Minister David Cameron told the court that a computer hard drive and memory sticks confiscated from David Miranda, the partner of Glenn Greenwald, a columnist for The Guardian, may contain the identities of intelligence officers. The adviser, Oliver Robbins, said in a written statement that the information could put the officers and their families at risk, or even make them vulnerable to recruitment by foreign intelligence services. The 13-page statement was the first detailed explanation that the government had provided for its detention of Mr. Miranda at Heathrow Airport on Aug. 18. He was questioned for nearly nine hours under terrorism legislation, and encrypted digital files he was carrying were seized. Mr. Greenwald has led the reporting on national security material leaked by Edward J. Snowden, the former contractor for the National Security Agency. Mr. Miranda, 28, was detained as he was bound for Brazil, where he and Mr. Greenwald live. He had met in Berlin with an American filmmaker who has been working with Mr. Greenwald on the N.S.A. coverage. Mr. Robbins, the deputy national security adviser on intelligence, security and resilience, said in the statement provided to the court that the government had so far viewed only a portion of the encrypted files seized from Mr. Miranda. In all, he said, the files contained about 58,000 highly classified documents, which were "highly likely to describe techniques which have been crucial in lifesaving counterterrorist operations, and other intelligence activities vital to U.K. national security." Allowing the material to become public, he said, "would do serious damage to U.K. national security and ultimately risk lives." The material included "personal information that would allow staff to be identified, including those deployed overseas," Mr. Robbins said. But no evidence for the assertions was provided during the hearing, prompting Mr. Miranda's lawyer and the editor of The Guardian, Alan Rusbridger, who sued last week to stop the police from viewing the material, to accuse the government of making unsubstantiated claims. "The defendant presented a smorgasbord of doomsday allegations without providing any specifics," Gwendolen Morgan, Mr. Miranda's lawyer, said in a telephone interview. In a statement, Ms. Morgan accused the government and the police of making "sweeping assertions about national security threats which they said entitled them to look at the materials seized, but they have said that they cannot provide further details in open court." "Mr. Miranda does not accept the assertions they have made," she added, "and is disappointed that the U.K. government is attempting to justify the use of terrorist powers by making what appear to be unfounded assertions." Mr. Rusbridger called Mr. Robbins's assertions inaccurate and asked why, if the material made public by Mr. Snowden presented such acute danger to national security, the government had done so little before detaining Mr. Miranda. "The way the government has behaved over the past three months belies the picture of urgency and crisis they have painted," he wrote on The Guardian's Web site. The government claims that they have at all times acted with the utmost urgency because of what they believed to be a grave threat to national security. However, their behavior since early June - when The Guardian's first Snowden articles were published - belies these claims. To give an example of what he views as the British government's lack of urgency, Mr. Rusbridger said in a statement that in late July The Guardian told the British authorities that some of the classified material it received from Mr. Snowden had been sent to The New York Times and ProPublica. This took place, he said, two days after The Guardian destroyed copies of documents provided by Mr. Snowden because the newspaper was facing threats of legal action by the British government. Mr. Rusbridger said weeks had passed before the British government contacted The Times. "We understand the British Embassy in Washington met with The New York Times in mid-August - over three weeks after The Guardian's material was destroyed in London," he said. To date, no one has contacted ProPublica, and there has been two weeks of further silence towards The New York Times from the government. A Times spokeswoman, Eileen Murphy, said, "Jill Abramson and Dean Baquet met with a British government representative in Washington." Ms. Abramson is the executive editor of The Times, and Mr. Baquet is the managing editor. "At the meeting, The New York Times was asked to relinquish classified material, a request that was declined," Ms. Murphy said.Under the interim injunction issued by the high court, investigators will be permitted to determine whether possessing the encrypted files could constitute a crime of "communication of material to an enemy" or a crime of communicating material about members of the military and the intelligence agencies that might prove useful for terrorists. The case will receive a full judicial review in late October.