The British government has been condemned internationally after the partner of Guardian journalist Glenn Greenwald was questioned for nine hours over Edward Snowden's NSA and GCHQ leaks.

Brazilian national David Miranda, who was in Heathrow airport en route to Rio de Janeiro, was held under the 2000 Terrorism Act - although Greenwald claims the interrogation had nothing to do with terrorism.

Instead, Greenwald claims the questions focused solely on his interviews with Snowden, in which a deluge of highly classified information about NSA and GCHQ surveillance programmes was leaked to the world.

Greenwald told the BBC World Service's Newsday programme: "They never asked him a single question at all about terrorism or anything relating to a terrorist organisation. They spent the entire day asking about the reporting I was doing and other Guardian journalists were doing on the NSA stories."

Miranda was reportedly questioned for nine hours, the maximum time permitted under the Terrorism Act. It is claimed that his phone, laptop and games console have been seized.

Amnesty International said the interrogation was "unlawful and inexcusable" and the Terrorism legislation was "abused for petty, vindictive reasons".

The Brazilian government is also enraged over the detention of Miranda and expressed "grave concern" at the use of the anti-terror laws.

"This measure is without justification since it involves an individual against whom there are no charges that can legitimate [sic] the use of that legislation. The Brazilian government expects that incidents such as the one that happened to the Brazilian citizen today are not repeated," said the Brazilian foreign ministry in a statement.

Experts suggest the detention of suspects under the Terrorism Act should last only a few hours; only in very rare and specific cases should it exceed six hours, and nine is almost unprecedented.

According to statistics from the Home Office, over 97% of examinations under schedule 7 of the Act last less than an hour and only one in 2,000 people are detained for six hours or longer.

Scotland Yard has refused to divulge the specifics of the detention but released a statement which reads, "At 08:05 on Sunday, 18 August a 28-year-old man was detained at Heathrow airport under schedule 7 of the Terrorism Act 2000. He was not arrested. He was subsequently released at 17:00."