"He said he was acting on behalf of the prime minster," Rusbridger said. "For about a period of a month, it was a cordial conversation."
But by mid-July, Rusbridger said, "it became an explicit threat of legal action if we didn't either return the disks or destroy them." The Guardian complied by destroying the hard drives.
"The point, which I explained to the British officials, was that Glenn Greenwald, the Guardian reporter, lives in Brazil," Rusbridger told CNN's Hala Gorani, who was sitting in for Christiane Amanpour. "He has a copy, and we already have another copy in America. So destroying a copy in London wasn't going to stop us from reporting."
Deputy Prime Minister Nick Clegg, who heads the Liberal Democrats, Cameron's coalition partners, considered the authorities' request "reasonable," his office said.
?"The Deputy Prime Minister felt this was a preferable approach to taking legal action," according to a statement issued Wednesday evening. "He was keen to protect the Guardian's freedom to publish, whilst taking the necessary steps to safeguard security."
Miranda was stopped as he was returning to the couple's Rio de Janeiro home after staying in Berlin with filmmaker Laura Poitras, who has been working with Greenwald on NSA-related stories.
Miranda has said he doesn't know what material he was carrying. He doesn't work for The Guardian, but the newspaper paid for his flights because he was helping his partner.
He and Greenwald told CNN's Anderson Cooper of their distress and anger about his treatment at Heathrow Airport.
"To start detaining people who they think they are reporting on what they're doing under terrorism laws, that is as dangerous and oppressive as it gets," said Greenwald.
Opinion: U.K. government and press collide in bullying of reporter's partner