The partner of the US journalist behind the Edward Snowden leaks launched legal action against Britain on Tuesday for holding him under anti-terror laws as the government admitted it was kept informed about his detention. David Miranda, a Brazilian national who has been working with his boyfriend Glenn Greenwald on the US intelligence leaks, was held and questioned for almost nine hours at London Heathrow Airport. The Guardian meanwhile said the British government had forced it to destroy files or face a court battle over its publication of US security secrets leaked by Snowden, who has been granted temporary asylum in Russia. "David Miranda is taking a civil action over his material and the way that he was treated," Guardian editor Alan Rusbridger, whose newspaper has worked with Greenwald and Snowden, told the BBC. British police confiscated Miranda's mobile phone, laptop, camera, memory sticks, DVDs and games consoles, according to The Guardian. "He wants that material back and he doesn't want it copied," Rusbridger said. The detention of Miranda, 28, has caused an international outcry and sparked protests from Brazil. He was travelling home to Rio de Janeiro from Berlin at the time and was held in a Heathrow transit lounge. The British government has faced questions about its involvement after the White House said it had received a "heads up" that police were about to arrest Miranda. Britain's interior minister, Home Secretary Theresa May, revealed she was briefed in advance of Miranda's detention, but said it was not for her to tell the police who they should or should not stop at airports. May said: "If it is believed that somebody has in their possession highly sensitive stolen information which could help terrorists, which could lead to a loss of lives, then it is right that the police act and that is what the law enables them to do." Prime Minister David Cameron's office also denied any political involvement. "The detention was an operational matter for the police. Number 10 was kept informed in the usual way," a Downing Street source told AFP on condition of anonymity. Mark Pritchard, a lawmaker for Cameron's Conservative party, defended the authorities. "The fact is they had concerns that there may have been somebody carrying sensitive material that may have directly or indirectly undermined our national security. And I'm glad the police took the action they did," he told BBC Radio 4. The legal firm acting for Miranda, Bindmans, said it was challenging the legality of Miranda's detention under Schedule 7 of Britain's Terrorism Act 2000, which applies to ports and airports, after being contacted on Sunday. Bindmans said it had written to the Home Office saying it would go to court this week if it did not receive assurances that "there will be no inspection, copying, disclosure, transfer, distribution or interference, in any way, with our client's data pending determination of our client's claim." The wider questions of state secrecy and the law intensified when Rusbridger made his claim about being ordered to destroy some of the Guardian's Snowden files. Writing in Tuesday's edition of the paper, Rusbridger said that two months ago he had been contacted by "a very senior government official claiming to represent the views of the prime minister". The call led to two meetings in which "he demanded the return or destruction of all the material we were working on". At the time, the paper was publishing a series of candid revelations about mass surveillance programmes conducted by the US National Security Agency and its British counterpart, GCHQ, after former NSA contractor Snowden handed them thousands of documents. Rusbridger claimed that in a call "from the centre of government", someone he does not identify told him: "You've had your fun. Now we want the stuff back." The editor said the government threatened to use the courts to try to obtain the leaked documents if the paper did not destroy them themselves. He said two GCHQ security experts oversaw "the destruction of hard drives in The Guardian's basement just to make sure there was nothing in the mangled bits of metal which could possibly be of any interest to passing Chinese agents." Rusbridger did not explain why he had waited a month to reveal the destruction of the computer equipment.