The partner of a Guardian journalist at the centre of revelations about US and British security services has spoken of being questioned by six agents on his "entire life" while travelling through Heathrow.
David Miranda was held by police 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.
Labour has called for an urgent investigation into the use of the powers to question Mr Miranda, who lives with reporter Glenn Greenwald, the journalist who interviewed American whistleblower Edward Snowden.
Arriving at Rio de Janeiro airport, Mr Miranda said: "I remained in a room. There were six different agents coming and going. They asked questions about my entire life, about everything.
"They took my 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."
Mr Miranda's flights are reportedly being paid for by the Guardian. A spokesman for the newspaper said: "David Miranda is not an employee of the Guardian.
"As Glenn Greenwald's partner, he often assists him in his work. We would normally reimburse the expenses of someone aiding a reporter in such circumstances."
A Downing Street spokesman said: "The Government takes all necessary steps to protect the public from individuals who pose a threat to national security. Schedule 7 forms an essential part of the UK's border security arrangements. But it is for the police to decide when it is necessary and proportionate to use these powers."