David Miranda will prepare a legal challenge over his detention at Heathrow Airport under terror legislation, the Guardian editor Alan Rusbridger has said.
Mr Miranda, 28, was detained at Heathrow Airport for nine hours under Schedule 7 of the Terrorism Act 2000 as he changed planes on a journey from Berlin to his home in Rio de Janeiro.
Mr Miranda, the partner of the Guardian journalist Glenn Greenwald, claimed he was detained by agents who questioned him about his "entire life" and took his "computer, video game, mobile phone, my memory card - everything".
Bindmans firm, who are representing Mr Miranda, announced in a statement released today that their solicitor Gwendoel Morgan had written to the Home Secretary and the Met Commissioner calling for assurances that "there will be no inspection, copying, disclosure, transfer, distribution or interference, in any way" of their client's data.
Mr Rusbridger told the BBC that Mr Miranda is launching a civil action against the Home Office over his detention and to prevent police from examining items he claims to have had seized.
Mr Rusbridger said the legal challenge would be mounted by Mr Miranda, not The Guardian, but the newspaper is "supportive” of it.
He said: "We will have to work out if that is legal or not, and that will be subject to legal challenge, I believe, by Glenn Greenwald and David Miranda because it's not clear that he was actually committing any offence in carrying material through Heathrow.
"I'm not aware of what that offence is."
He went on: "I think there will be a legal challenge to the use of this very controversial bit, this Schedule 7, of the Terrorism Act and its use to obtain journalistic material.
"A lot of journalists the world over fly through Heathrow and I think some of them now are going to be quite anxious about how the British authorities regard this bit of Britain that is not quite Britain but is Britain."
Asked if The Guardian would also mount any challenge, he said: "At the moment this is a legal challenge by David Miranda, who is the individual, and he has lawyers who will mount that challenge."
In piece written for the paper yesterday, Mr Rusbridger also alleged Whitehall figures were sent to destroy hard drives owned by the newspaper after being asked to destroy all material related to Edward Snowden.
Last night Scotland Yard said the detention was subject to a “detailed decision-making process”, saying: “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 Metropolitan Police Service at this time.”
David Anderson QC, the independent reviewer of terrorism legislation, has asked for an official briefing on the arrest. He will meet with police later to discuss what he described as an “unusual case”.
The announcement comes as a source at Downing Street denied the Government has any political involvement in Mr Miranda's detention, and said it was "kept abreast of the operation in the usual way".
"The Government does not direct police investigations," they added.
Schedule 7 applies only at airports, ports and border areas, allowing officers to stop, search, question and detain individuals.