Departing from the core of the rule of law? The ends always justify the means.
You can understand the judges' concerns when a quick Google turns up nothing of any substance on either Erol Incedal, formerly AB, or Mounir Rarmoul-Bouhadjar, CD. The latter seems to have a LinkedIn profile, while Incedal doesn't have so much as that. As well as revealing their identities, the judges also ordered that most of the opening of the trial be held in public, including a portion of the judge's introductory remarks and a portion of the prosecution's opening statement. Additionally, a number of "accredited journalists" will be allowed to sit in on the majority of the closed proceedings, although they will only be allowed to report something of what they witness once the trial has concluded and a further review has taken place.
If all this is meant to seem as though an attempt at compromise has been made, that's precisely what the government hopes it will be seen as. Mr Justice Nicol rejected the idea of "accredited journalists" initially on the grounds of practicality, as the idea was proposed in the certificates signed by the secretaries of state. It seems to be the only part of the ruling he got right: as the Graun puts it, this is an absurdity, a "kind of time-lapse justice without guarantees". It in effect makes the (un)lucky chosen hacks complicit in the secrecy, unable to know if their account of the trial will appear or not.
We must of course recognise that four judges have now seen the evidence from the CPS and concluded that on balance it is better for justice to be attempted, even in secret, than see the prosecution not proceeded with. The latest three say the case is "exceptional". Perhaps it is. There are circumstances when such secrecy certainly could be justified; the problem is we cannot make a judgement on whether in this instance it is justified when we will still know so little of the case against the men. The only recent precedent was the case of Wang Yam, whose defence to the charge of murder was held in camera after he claimed to have some connection with the security services. Clearly, he did have some link with them, but it didn't prevent his conviction, nor can we know what his defence was. Yam is currently appealing to the ECHR on those very grounds.
If this departure from open justice, the "core of the rule of law" as Lord Bingham had it, seems odd in the same week as David Cameron was defining it as a fundamental British value, then it shouldn't. The government and the security services have always made things up as they go along, will always make things up as they go along. We can't know why they are so insistent this case has to remain secret, although we can certainly guess that it has to be either supremely embarrassing or has only reached court due to profound security service involvement. The problem is once ministers and the agencies get into the habit of favouring secrecy over openness the ever more likely they are to resort to it again. Justice must be seen to be done, but it must also be seen to be fair. In this instance the case for secrecy has simply not been made, and once again the state seems to be demanding of others what it won't accept of itself.