The Guardian journalist whose partner was detained for nine hours under anti-terror laws at Heathrow Airport has given his first British TV interview to ITV News, revealing he is "angry" but "not surprised" by the police's action.
Glenn Greenwald, who has run a series of stories on US surveillance based on leaked files, told Brazil Correspondent Nick Ravenscroft the goal of police who held his partner David Miranda without access to a lawyer was "to be thuggish and [to] intimidate" rather than to question him.
Watch Brazil Correspondent Nick Ravenscroft's report:
Mr Miranda's lawyers have written to Home Secretary Theresa May and Met Police Commissioner Bernard Hogan-Howe to express concern about his "unlawful" detention and to demand files confiscated by police are returned.
Speaking at his home in Rio de Janeiro, Mr Greenwald refused to confirm the nature of the data his boyfriend had been carrying ahead of a return flight to Brazil.
But he told ITV News "even the most advanced intelligence services" would find it "impossible" to access information that he and Mr Miranda carry across the world because it is too well encrypted.
Mr Greenwald rejected claims that Mr Miranda posed any form of terror threat by carrying allegedly leaked data, saying not a "single comma" from his whistleblowing reports about state security has aided terrorism.
Earlier Theresa May broke from her holiday to confirm she had had been briefed in advance of Sunday's detention, but insisted she had not ordered it as she plays no part in who the police do and do not stop.
Ms May, though, endorsed the officers' actions, saying:
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.
A Downing Street source said the Prime Minister was also "kept abreast of the operation" to detain Mr Miranda, but again denied there was any political involvement in the move, adding: "The Government does not direct police investigations."
The detention, though, was ridiculed by Guardian editor-in-chief Alan Rusbridger, who told ITV News it was something out of an "Alice in Wonderland world" and a "misuse of a terror law to inhibit journalism".
Watch: Guardian editor Alan Rusbridger's interview:
Mr Rusbridger also confirmed he was ordered by a senior Whitehall official to destroy material on a laptop that was regarded as threatening to national security.
He claimed security officials were worried about Chinese and Russian agents "surrounding" the Guardian's London headquarters.
Mr Rusbridger said given the newspaper already had copies of the information in Brazil and America, the request made helped to conjure up "one of the more bizarre days in Guardian history".
Meanwhile, a petition launched by Four Lions actor Adeel Akhtar calling for the Government to look urgently at the terrorism laws used to detain Mr Miranda has been backed by more than 45,000 names.
Miranda was detained at Heathrow Airport under Schedule 7 of the Terrorism Act 2000 on Sunday as he changed planes on a journey from Berlin to his home in Brazil.