MercoPress. South Atlantic News Agency

PM Cameron’s office was ‘kept abreast’ with the decision to detain Greenwald’s partner

Miranda is taking action to challenge the legality of his detention at Heathrow under terrorism legislation

The Prime Minister’s office, 10 Downing Street, was “kept abreast” of the decision to detain David Miranda, the partner of Guardian journalist Glenn Greenwald who has written about US and British surveillance programs based on leaks by Edward Snowden, a spokesperson has revealed.

Brazilian national Miranda was held at Heathrow for nine hours on Sunday, while in transit from Germany to Brazil where he lives with Greenwald. He has launched a legal challenge over the police's use of anti-terror laws to detain him and seize his property. But the Home Office said police must act if they think someone has “stolen information that would help terrorism”.

The No 10 spokesman did not confirm whether PM David Cameron had been informed. But Conservative MP and former shadow home secretary David Davis said he “almost certainly” would have been.

The Metropolitan Police Service (MPS) said in a statement the examination of the 28-year-old Brazilian was “necessary and proportionate” and he had been offered legal representation and was attended by a solicitor.

Greenwald 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.

Miranda said he was held in a room and questioned by six agents about his “entire life”. They confiscated his laptop, an additional hard drive, two memory sticks, a mobile phone, a smart watch and a video games console, his lawyers said.

He was required to divulge the passwords to his personal computers, phone and encrypted storage devices, they added.

In Germany, Miranda had been staying with US film-maker Laura Poitras, who has also reportedly been working on the Snowden files with the Guardian. DVDs of two of her films - The Oath and My Country, My Country - were also seized at Heathrow, the lawyers added.

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.

He is now taking action to challenge the legality of his detention, and to try to prevent the police from examining the electronic items they seized from him.

His 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”.

The opposition Labour Party also urged the authorities to explain how they could justify using the Schedule 7 measure in the case of Miranda, and rights activists accused the authorities of harassing anyone connected to Snowden.