David Miranda in legal challenge over seized data

David Miranda was in transit when he was detained at Heathrow Airport

David Miranda, the man held at Heathrow for nine hours on Sunday, is taking legal action to prevent the police from examining the electronic items seized.

Mr Miranda, the partner of Guardian journalist Glenn Greenwald, was held at the airport under the Terrorism Act.

His solicitors say he is challenging the legality of his detention.

The Home Office has defended the detention, saying police must act if they think someone has "stolen information that would help terrorism".

Law firm Bindmans have written to the home secretary and Met Police commissioner for assurances "there will be no inspection, copying, disclosure, transfer, distribution or interference, in any way, with our client's data pending determination of our client's claim".

'Duty to protect'

The detention of Mr Miranda, 28, has been condemned by senior British politicians, human rights organisations and the Brazilian authorities.

The UK's independent reviewer of terrorism legislation, David Anderson QC, has said the length of detention was "unusual" and will meet police later.

Brazilian Mr Miranda was held at Heathrow on his way from Berlin to Rio de Janeiro - where he lives with Mr Greenwald.

The reporter has broken most of the stories about state surveillance based on the leaks from fugitive Edward Snowden, who used to work at the US National Security Agency.

Guardian editor Alan Rusbridger: "l think it is suspicious that he was stopped at Heathrow..."

Mr Miranda 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.

Scotland Yard maintained that its use of the Terrorism Act to detain Mr Miranda was "legally and procedurally sound".

A Home Office spokesperson said: "The government and the police have a duty to protect the public and our national security.

"If the police believe that an individual is in possession of highly sensitive stolen information that would help terrorism, then they should act and the law provides them with a framework to do that. Those who oppose this sort of action need to think about what they are condoning."

'Worldwide outcry'

Mr Miranda claimed he was held for nine hours by agents who questioned him about his "entire life" and took his computer, video games, mobile phone and memory cards.

In Germany, Mr Miranda had been staying with US film-maker Laura Poitras, who has also been working on the Snowden files with Mr Greenwald and the Guardian.

The paper said Mr Miranda was stopped while he was "ferrying materials" between his partner and Ms Poitras.

In an interview with the BBC, Guardian editor Alan Rusbridger said there had been a "worldwide outcry" at the use of the Terrorism Act to hold Mr Miranda.

"This act enables people to interrogate people for up to nine hours and seize all their belongings with no checks and balances."

The US government has said British officials gave it a "heads up" about Mr Miranda's detention but said the decision to seize him was a British one taken "independent of our direction".