The partner of the US journalist behind the Edward Snowden leaks launched legal action against Britain 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 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.

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 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.

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 whom 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.

Greenwald told CNN he had no evidence that the US ordered the detention, but that he was "disturbed my government was aware of this foreign country's intent to detain my foreign partner and did nothing to discourage it."

But he dismissed as "completely inaccurate" a quote attributed to him vowing to target the British government as revenge for the detention.

In the same joint interview, Miranda spoke of his "relief" after finally arriving in Brazil.

"I knew I would be protected here because I was in my country," he explained.

The legal firm acting for Miranda, Bindmans, said it was challenging the legality of the detention under Schedule 7 of the 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 Daily Mail and Independent newspaper both reported on Wednesday that the official was Jeremy Heywood, Britain's top civil servant.

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 Guardian 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.

He said two GCHQ security experts oversaw "the destruction of hard drives in The Guardian's basement."

Rusbridger did not explain why he had waited a month to reveal the destruction of the computer equipment.

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