A major terrorism trial is to be heard in secret, the Court of Appeal has heard.
Media organisations had launched a challenge to orders made by Mr Justice Nicol on May 19 at the Old Bailey in relation to the trial of two defendants who can only be identified as AB and CD.
Counsel Anthony Hudson said today: "The Crown has sought and obtained an unprecedented order that the trial of two defendants charged with serious terrorism offences should take place entirely in private with the identity of both defendants withheld and a permanent prohibition on reporting what takes place during the trial and their identities."
Lord Justice Gross, Mr Justice Simon and Mr Justice Burnett said they would give their decision on the appeal in a few days.
Mr Hudson said the appeal raised important issues relating to the constitutional principle of open justice but also the equally important principle of fairness and natural justice.
"This case is a test of the court's commitment to that constitutional principle in the admittedly difficult and sensitive circumstances where the state seeks to have trials involving terrorism held in secret and relies, in support of that, on grounds of national security."
He said it was fully accepted that Mr Justice Nicol and the appeal judges had a very difficult exercise to carry out.
Mr Hudson said that, as far as he was aware, no order had ever been made which required an entire criminal trial to be held in private with the media excluded and the defendants anonymised.
This required the "most anxious scrutiny" by the Court of Appeal.
"We submit that the orders made mark such a significant departure from the principle of open justice that they are inconsistent with the rule of law and democratic accountability."
Richard Whittam QC, for the Crown, said it supported open justice but the court was aware of the exceptional circumstances that had led to exceptional procedures in the case.