The publication of material leaked by Edward Snowden is capable of being an act of terrorism, the home secretary's barrister has said.
The claim was made in legal papers in a High Court case in which the partner of Guardian journalist Glenn Greenwald is challenging his detention at Heathrow in August under anti-terror laws.
David Miranda was carrying data files for Mr Greenwald who has covered data leaked by US whistleblower Mr Snowden.
He says his detention was unlawful.
The two-day judicial review action is being contested by the home secretary and the Metropolitan Police.
Mr Miranda was en route from Berlin to Rio de Janeiro on 18 August when he was detained, questioned and searched by police at Heathrow under Schedule 7 of the Terrorism Act 2000.