LONDON (Reuters) - Leaks by a fugitive U.S. intelligence contractor have damaged Britain's national security, and the data he gave journalists includes information that might expose the identities of British spies, a government official told the High Court in London.
The official said Brazilian David Miranda, the partner of a Guardian newspaper journalist, was carrying a computer hard-drive containing 58,000 highly classified intelligence documents when he was detained at Heathrow airport earlier this month.
Miranda's partner Glenn Greenwald has led the Guardian's coverage of leaks from Edward Snowden, a former contractor at the U.S. National Security Agency (NSA), about U.S. and British surveillance of phone and Internet users.
In a written statement to the court at Friday's hearing, Oliver Robbins, Britain's Deputy National Security Adviser for Intelligence, Security and Resilience, said media stories about the documents seized from Miranda had already caused harm.
"It is worth reiterating the point that real damage has in fact already been done to UK national security by media revelations," he said.
"A particular concern for HMG (the British government) is the possibility that the identity of a UK intelligence officer might be revealed. It is known that contained in the seized material is personal information that would allow staff to be identified, including those deployed overseas."
He also said that Miranda and others had shown "very poor judgement in their security arrangements" by making passwords to the material easily accessible.
Miranda's lawyer, Gwendolen Morgan, accused UK authorities of making "sweeping and vague assertions about national security."
Snowden set off an international furore when he told newspapers in June that the NSA was mining the personal data of users of Google, Facebook, Skype and other U.S. companies under a secret programme codenamed Prism. Facing espionage charges at home, he has taken temporary asylum in Russia.
Outrage among privacy campaigners and the media was fuelled when British authorities used anti-terrorism laws to detain Miranda for nine hours when he stopped off at Heathrow on August 18 on his way home to Brazil from a trip to ferry materials between Greenwald and a film maker in Berlin.
Guardian editor Alan Rusbridger said Robbins had made "a number of unsubstantiated and inaccurate claims".
"The Guardian took every decision on what to publish very slowly and very carefully," he said, adding he was dismayed by the government's "blurring of terrorism and journalism."
Miranda, who returned to Brazil after being released by officers, had asked the London court to issue an injunction stopping police from examining the material.
But the court heard on Friday that lawyers representing him and the British authorities had agreed to give British police and the interior ministry until October - when a review will be held - to continue examining the seized data.
The decision prolongs a High Court ruling last Thursday that the data could be examined on counter-terrorism and national security grounds only, with further extension given on Friday under legislation designed to protect state secrets.
London's Metropolitan Police Service (MPS) welcomed Friday's court decision, saying in a statement that it needed to sift through the highly sensitive material to protect public safety.
Caroline Goode, a counter-terrorism detective, said in a witness statement released to the media that their investigations could stretch around the world.
"It is likely that the MPS is investigating a conspiracy with a global dimension. It is necessary to ascertain if the stolen, classified material has been disseminated."
Editing by Mark Trevelyan