Image copyright Getty/AFP Image caption David Miranda was detained at Heathrow in August

Journalism is no defence when it comes to the possession of stolen state secrets, the High Court has been told.

Judges are examining claims police unlawfully detained David Miranda, partner of former Guardian journalist Glenn Greenwald, at Heathrow Airport.

Mr Greenwald has written a series of stories about state surveillance based on leaked documents.

The Home Office argues officers were right to hold and seize material from Mr Miranda on 18 August.

Analysis What is terrorism and who is a terrorist? Certainly not responsible journalism carried out by responsible journalists, say lawyers for David Miranda. But it was under terrorism laws that he was arrested at Heathrow and his phone, laptop and other equipment seized. The government says the secret material could get into the wrong hands - al-Qaeda for example - and that in itself amounts to terrorism under its wide ranging definition in British law. Ignorance is no defence, runs this argument, and who are journalists to determine that risk? Nobody disputes that MI5 wanted to get its hands on the material Mr Miranda was carrying. What is disputed is the way, and under which law, it did so.

Mr Greenwald wrote his articles on US and UK spying after receiving material from Edward Snowden, the former National Security Agency contractor who is now in Moscow after seeking sanctuary from the US following the leaks.

'Just rhetoric'

Steven Kovats QC, representing the home secretary, told the court the secret material taken from Mr Miranda could have ended up in the hands of al-Qaeda.

Mr Miranda's lawyers say the detention at Heathrow was illegal because it was carried out under the wrong law: Schedule 7 of the Terrorism Act 2000.

They argue that in reality he was detained on the say-so of the security services so they could seize journalistic material.

But Mr Kovats told the court: "In broad terms there is more to terrorism than letting off bombs."

He added that describing oneself as a "responsible journalist" did not mean one understood the significance of the material in question.

Judge Lord Justice Laws replied: "I don't really know what is meant by the term 'responsible journalist'.

"It doesn't make a journalist omniscient in security matters."

"It's just rhetoric really."

The hearing continues.