Scotland Yard has said that the detention of the partner of a Guardian journalist at the centre of revelations about US and British security services was "legally and procedurally sound".
It has also denied allegations that he was not given access to a lawyer.
David Miranda said he was questioned by six agents on his "entire life" while being held at Heathrow airport under terror laws for nine hours - the legal limit before a suspect must be charged or released - as he changed planes on a journey from Berlin to his home in Brazil.
Miranda is to mount a legal challenge over his detention at Heathrow Airport under terror legislation, Guardian editor Alan Rusbridger said.
Mr Miranda, partner of Guardian journalist Glenn Greenwald, was detained at Heathrow Airport under Schedule 7 of the Terrorism Act 2000 as he changed planes on a journey from Berlin to his home in Brazil.
Greenwald - the reporter who interviewed American whistle-blower Edward Snowden - called Mr Miranda's detention a "profound attack on press freedoms and the news-gathering process".
"To detain my partner for a full nine hours while denying him a lawyer, and then seize large amounts of his possessions, is clearly intended to send a message of intimidation to those of us who have been reporting on the NSA (US National Security Agency) and GCHQ," he said.
However, the Metropolitan Police said the use of the Terrorism Act to detain Mr Miranda was "legally and procedurally sound".
Scotland Yard said in a statement issued last night: "The examination of a 28-year-old man under Schedule 7 of the Terrorism Act 2000 at Heathrow Airport on Sunday 18 August was subject to a detailed decision making process.
"The procedure was reviewed throughout to ensure the examination was both necessary and proportionate.
"Our assessment is that the use of the power in this case was legally and procedurally sound.
"Contrary to some reports the man was offered legal representation while under examination and a solicitor attended. No complaint has been received by the Metropolitan Police Service at this time."
White House spokesman Josh Earnest said the British government gave the United States advance notice that London police intended to detain Mr Miranda but added that the US did not request the detention and was not involved in the decision.
Labour called for an urgent investigation into the use of the powers to question Mr Miranda after he said agents took his "computer, video game, mobile phone, my memory card. Everything".
Mr Miranda was stopped at 8.30am on Sunday when returning from a trip to Berlin. He was questioned under schedule 7 of the Terrorism Act 2000 which applies only at airports, ports and border areas, allowing officers to stop, search, question and detain individuals.
Shadow home secretary Yvette Cooper said: "Any suggestion that terror powers are being misused must be investigated and clarified urgently - the public support for these powers must not be endangered by a perception of misuse."
David Anderson QC, the independent reviewer of terrorism legislation, has asked for an official briefing on the arrest, which he described as an "unusual case".
He told BBC Radio 4's 'The World At One' that around two million people pass through UK ports every year.
"Of those, 60,000-70,000 are examined under this schedule 7 stop and only 40 of those are actually kept for longer than six hours," he said.
"So you can see what an unusual case this was, if it's correct that Mr Miranda was held right up to the nine-hour limit."
Downing Street said the case was an "operational matter for the police".
Bob Satchwell, executive director of the Society of Editors, said it was difficult to avoid the conclusion that the move was an attempt to intimidate a journalist.
He said: "Journalism may be embarrassing and annoying for governments but it is not terrorism. It is difficult to know how in this instance the law was being used to prevent terrorism.
"On the face of it, it is difficult to avoid the conclusion that the detention of a journalist's partner is anything other than an attempt to intimidate a journalist and his news organisation that is simply informing the public of what is being done by authorities in their name.
"It is another example of a dangerous tendency that the initial reaction of authorities is to assume that journalists are bad when, in fact, they play an important part in any democracy."
Since June 5, Mr Greenwald has written a series of stories revealing the NSA's electronic surveillance programmes.
The newspaper also published stories about blanket electronic surveillance by Britain's GCHQ, also based on documents from Mr Snowden.
During his trip to Berlin, Mr Miranda visited Laura Poitras, a US film-maker who has been working on the Snowden files with Mr Greenwald and the Guardian.
Michelle Stanistreet, general secretary of the National Union of Journalists, said the detention of Mr Miranda "points to the growing abuse of so-called anti-terror laws" in the UK.
"His detention and treatment was a gross misuse of the law and clearly linked to the work of his partner Glenn Greenwald, who revealed the extent of mass surveillance and wholesale interception of internet traffic by the US security services and its collusion with GCQH.
"The treatment meted out to David Miranda is wholly unacceptable and it is time the use, or rather misuse, of terrorism legislation as a way of targeting individuals was properly and independently reviewed."
Liberty director Shami Chakrabarti said: "David Miranda's chilling nine-hour detention was possible due to the breathtakingly broad Schedule 7 power, which requires no suspicion and is routinely abused.
"People are held for long periods, subject to strip searches, saliva swabbing and confiscation of property - all without access to a publicly funded lawyer.
"Liberty is already challenging this law in the Court of Human Rights but MPs disturbed by this latest scandal should repeal it without delay."