It is not clear whether later phases of the case will be opened to the public - the BBC has submitted a written argument that it should be.

As well as the BBC, journalists from the Guardian, the Telegraph, PA, Bloomberg, and Computer Weekly attended the Royal Courts of Justice but were not admitted into the court room.

Sir James Eadie KC, who previously represented the government in significant cases such as Shamima Begum's citizenship appeal, was seen entering the hearing.

On Thursday, five US politicians from across the political divide urged the court to remove what they call the "cloak of secrecy" surrounding the row - which they say has major security implications.