Using the Terrorism Act to detain the partner of a Guardian reporter who wrote about US and UK security services was “legally and procedurally sound”, Scotland Yard has said.
It was responding to claims it misused its powers by holding David Miranda for nine hours at Heathrow on Sunday.
Independent reviewer of terrorism legislation David Anderson QC has said the length of detention was “unusual”.
Anderson will meet police later for an urgent briefing on the matter.
He has been joined by senior British politicians in calling on police to explain why Miranda, 28, was detained.
The Brazilian was held at Heathrow on his way from Berlin to Rio de Janeiro, where he lives with his partner, Guardian journalist Glenn Greenwald, who has published information from US whistleblower Edward Snowden.
He was detained under schedule 7 of the Terrorism Act 2000. This allows police to hold someone at an airport, port or international rail station for up to nine hours for questioning about whether they have been involved with acts of terrorism
Miranda said he was kept in a room and questioned about his “whole life”.
Scotland Yard, which has not revealed on what grounds he was detained, said in a statement on Monday night that the “examination” of Miranda was “subject to a detailed decision-making process”.
“The procedure was reviewed throughout to ensure the examination was both necessary and proportionate,” it added.
“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 MPS at this time.”
In Germany, Miranda had been staying with US film-maker Laura Poitras, who has also been working on the Snowden files with Greenwald and the Guardian, according to the newspaper.
The paper said Miranda was stopped while he was “ferrying materials” between his partner and Poitras.
“I was kept in a room with six agents coming in and out and asking me about everything – my whole life,” Miranda told reporters when he arrived back in Brazil on Monday.
“They took my computer, my video games, my mobile phone and memory cards – everything.”
In a separate interview with the Guardian, he said: “They were threatening me all the time and saying I would be put in jail if I didn’t co-operate.
“They treated me like I was a criminal or someone about to attack the UK… it was exhausting and frustrating, but I knew I wasn’t doing anything wrong.”
The US government has said British officials gave it a “heads up” about Miranda’s detention but said the decision to seize him was a British one taken “independent of our direction”.
Brazil’s foreign minister Antonio Patriota has called the detention “not justifiable” and has sought answers from his UK counterpart, William Hague.
Downing Street has said the case is an “operational matter for the police”.
Greenwald said the British authorities’ actions amounted to “bullying” and linked it to his writing about Snowden’s revelations concerning the US National Security Agency (NSA).
Snowden, who has been granted temporary asylum in Russia, leaked details of extensive internet and phone surveillance by American intelligence services.
According to the Guardian, he passed “thousands of files” to Greenwald, who has written a series of stories about surveillance by US and UK authorities.
Greenwald said his partner’s detention was “clearly intended to send a message of intimidation to those of us who have been reporting on the NSA and [UK intelligence agency] GCHQ”.