Image copyright Julia Quenzler Image caption Erol Incedal's retrial took place at the Old Bailey in March last year

BREAKING: Reporter can't tell you what's happened.

Possibly the worst headline I've ever written. But before I'm accused of completely failing to perform basic contractual duties, allow me to explain why those seven words are rather important.

Since 2013, the BBC and almost every other leading news organisation in the UK has been locked in a bizarre battle to tell you the truth about Erol Incedal.

"Who he?" I hear you ask. He's a student from London who was accused of preparing some kind of major terrorism plan. And then after two trials he was found not guilty of that allegation. But I can't tell you why.

The prosecution of Erol Incedal has been, without a shadow of a doubt, the strangest criminal trial that those of us who report on the law have ever seen.

Apologies. I meant to write "not really seen much of" because almost all of what happened was behind closed doors.

And now the Court of Appeal has ruled that the unprecedented gagging order in the case will remain in place forever.

Incedal was charged with another man, Mounir Rarmoul Bouhadjar, in October 2013. Rarmoul Bouhadjar admitted possessing bomb-making plans. Incedal denied the allegation, saying he had a reasonable excuse for holding them. In 2014, a jury convicted him of that, but they failed to agree whether he was guilty of a more serious charge of preparing an act of terrorism. At a retrial the following year, a fresh jury cleared him.

I don't know why that jury cleared him. If I did, I couldn't tell you. Some of my colleagues do however know. But they can't tell me. Or you. They'd be in Contempt of Court and could end up in prison.

Erol Incedal's trials involved an unprecedented level of secrecy in courts that are normally open to the public. There were brief periods of public evidence and then slightly longer periods when a group of accredited journalists were allowed in to listen to some of the mysterious evidence. The third and highest level of the case operated in complete secrecy, with the media totally banned.

At the end of each secret session that journalists could attend, police took their notebooks and put them in a safe. Where are those notebooks now? You know that scene at the end of Raiders of the Lost Ark in which anonymous officials lock away Indiana Jones's greatest discovery? You get the idea.

How secret was the secret trial?

First trial autumn 2014. Jury failed to reach a verdict on preparing acts of terrorism

Second trial February - March 2015

Approximately 68 hours of evidence

10 of them in open and public court

28 hours of secret evidence heard by "accredited journalists" - but remains secret until a legal ruling otherwise

30 hours of evidence heard in complete secrecy before judge, lawyers and jury

And that's been the whole point of this legal battle - to try to find some way to peel the legal gaffer tape from my colleagues' mouths.

At the earliest stage of proceedings in 2013, the Crown Prosecution Service (CPS) sought anonymity for the defendants.

Both the home and foreign secretaries had raised concerns with the CPS. lt later told the trial judge, Mr Justice Nicol, that should the "factors of concern be ventilated in a public trial", the prosecution would be "presented with representations" to drop the charges on grounds of national security.

Mr Justice Nicol ruled the case would be prosecuted "in camera". There would be a jury, as ever, but they would never be able to disclose what they heard. The Court of Appeal later modified that to allow journalists to attend some of the hearings - but with no guarantee that anything would ever become reportable.

So given those journalists still can't speak, and Erol Incedal can't say why he was acquitted of preparing an act of terrorism, is this a massive outrage to justice in a democracy?

Well, the Court of Appeal says not.

The general principle is that justice must be seen to be done - but the law also says there can be myriad good reasons to withhold information from the public - not least for the protection of vulnerable witnesses and victims.

In the case of Erol Incedal, Lord Thomas, the Lord Chief Justice, said in Tuesday's Court of Appeal ruling the nature of the evidence was such that the trial judge had to lock the court's doors.

He and two other senior judges ruled that the trial judge had rightly considered that the national security material in the case had to be protected at all costs.

The Court of Appeal judgement recognises that secret hearings compromise the media's role in holding power to account: if justice cannot be seen to be done, how does one know if it is justice?

Lord Thomas offers the suggestion that the Intelligence and Security Committee could fill some of that vacuum - although it is, also, a semi-secret body.

So what happens now?

While the media gag is legal, the subtext of the Court of Appeal judgement makes clear that it doesn't want courts to lightly enter into the unique arrangements seen in the Incedal case.

Secondly, the judge fired a warning shot of sorts over the bows of MI5 and MI6. If the agencies were ordered in the future to disclose information for use in criminal trials, and the prosecutors want to go ahead, they cannot simply say no and remain in the shadows.

On the face of it, that is a pretty obvious statement that government and its agencies are not above the law - but it is also a clear sign that the next time a case like this comes up, the very high legal test for withholding information from the public remains in play.

Does that mean it will never happen again? Not at all. My instincts and experience make me suspect this won't be the last trial of its kind.