A mixture of tribunal fatigue and the prominence given to the government reshuffle, the queues at the passport office and the ongoing church sex abuse scandal ensured that developments at the Moriarty tribunal last week barely registered with the majority of the public.

However, what emerged was nothing short of sensational. It raised questions, not just about the credibility of the Moriarty tribunal, but the whole tribunal of inquiry process.

The tribunal, set up to investigate payments to Charlie Haughey and Michael Lowry, has been operating at Dublin Castle for nearly 13 years at huge cost to the taxpayer.

Last week, however, was by some distance its worst in all that time. The issues, inevitably, are complex. But the most important point is that a few weeks ago, the tribunal was on the verge of publishing its final report into the awarding of the second mobile phone licence. That report would have contained some central and key findings that, following new evidence from two officials from the Office of the Attorney General in recent days, surely will not now be in the final report.

This inevitably raises question marks about the tribunal because it had strongly resisted hearing this new evidence, which has proven to be clearly relevant.?It finally relented in recent weeks under the threat, it is claimed, of legal action.

What if this evidence had not been heard and the final report had been published, as very nearly happened? It's a question that goes to the very heart of how tribunals, and the Moriarty tribunal in particular, operate.

Judge Michael Moriarty said last week in response to the strong interventions from counsel for various interested parties, including very significantly the Department of Communications, that he had never claimed he was infallible.

That, of course, is true. But the reality is that, rightly or wrongly, the findings of a tribunal have generally been treated as infallible, particularly in the media. Until now at least.

There are legal restrictions on the media from reporting on the contents of the tribunal's preliminary or provisional findings, which have been issued to affected parties.

But Denis O'Brien is on the record as saying that the Moriarty tribunal has made a provisional finding that the licence was issued illegally to Esat Digifone.

This finding is based on a change of ownership in the O'Brien-led Digifone consortium that took place after it was selected as preferred bidder in 1995, but before being formally awarded the licence the following year.

Businessman Dermot Desmond's IIU had taken the 20% stake in the consortium initially pencilled in for institutional investors.

At the time, the Department of Communications sought advice from the Office of the Attorney General on this change in the ownership make-up, with the latter in turn seeking advice from senior counsel Richard Nesbitt.

After much pressure from the state and other parties, Nesbitt was called to the witness box in 2009.

Along with stating that the matter had been covered by his written advice, he said he also had a "crystal clear" recollection of giving oral advice that the ownership change was not a barrier to issuing the licence.

This was challenged as "not credible" by tribunal senior counsel John Coughlan, to which Nesbitt replied that he had not come into the witness box to give incorrect evidence.

Even at the time, it was a surprising clash, not least because one senior counsel accusing another of giving evidence that was "not credible" would be seen as 'just not cricket' in the rarified surroundings of the law library.

The tribunal legal team's scepticism surrounding the nature of the legal advice given by Nesbitt to the Attorney General's office/department seems also to have been reflected in Judge Moriarty's revised provisional findings.

However, following the last-minute decision to bow to pressure and call the two officials from the Office of the Attorney General – John Gormley and Denis McFadden – Nesbitt's version of events appears to have been entirely vindicated.

The two officials said that the Nesbitt opinion was regarded by the Attorney General's office as dealing with the ownership issue.

They backed up what Nesbitt said about giving oral evidence. And that, in turn, backed up the Department of Communications officials who said that following this advice, there was no problem in awarding the licence to Esat Digifone.

But it was worse than that for the tribunal. It emerged in recent weeks that the tribunal's legal team had met privately with the two officials from the Attorney General's office and Nesbitt as long ago as 2002 and were told that Nesbitt's advice dealt with the ownership issue and approved the issuing of the licence.

Incredibly, this meeting was not known to most parties involved in the tribunal until statements were circulated in recent weeks just prior to Gormley and McFadden giving evidence.

Gerard Hogan, senior counsel for Dermot Desmond, said last week it was a "very surprising turn of events" that for seven or eight years, a number of parties were under the impression that no such advice had been given.

This led, Hogan argued, to a whole line of inquiry that was based on a false premise.

After all, when Nesbitt gave evidence to the tribunal last year, it was put to him that it was the first time he had ever claimed his advice covered the ownership issue.

"Mr Nesbitt's credibility was being impugned on the basis that he had only, so to speak, recently come up with this explanation," Hogan said, adding that the proposition should not have been put to the witness because this explanation had been given to the tribunal in 2002.

How could this have happened? The senior counsel representing the Department of Communications has said it was the department's view that the evidence was not accepted because it differed from the tribunal's "working hypothesis" on the matter.

The evidence represented "an inconvenient truth" for the tribunal. Whether or not this is the case, the very fact this argument has been made at all is hugely serious for the tribunal.

Even worse for the tribunal, Judge Moriarty admitted last week that he made an error when he said in February 2008 that the Attorney General had confirmed in writing that the legal advice given by Nesbitt in 1996 did not address the change of ownership.

It has emerged that the Attorney General's office wrote to the tribunal on at least seven occasions saying there was no such letter.

This was one of two "significant errors", Moriarty admitted last week, that the tribunal had made – the second being not circulating the memo on the 2002 meeting between the tribunal's legal team and the officials from the Attorney General's office.

And there was further embarrassment for the tribunal during evidence given by McFadden about the private meeting in 2002 that Gormley, Nesbitt and McFadden had with the tribunal legal team.

McFadden revealed that, during the meeting, Jerry Healy for the tribunal described Nesbitt's opinion as "sh**e".

The use of such language brought to mind a comment previously made by Supreme Court judge Susan Denham in 2004 in relation to the Moriarty tribunal.

In a judgement that found in favour of the Moriarty tribunal in a case taken by Dermot Desmond, Judge Denham very pointedly said she was "concerned at some of the references made in the language of counsel for the tribunal... In conducting such an inquiry persons working for the public should adhere to a code of good manners in relation to the witnesses they are questioning."

There was also a bizarre incident during McFadden's evidence when John Coughlan denied he had attended the meeting of October 2002. "I know what I was doing at the moment". McFadden insisted Coughlan had been there and later minutes were produced showing McFadden was correct.

Where does all of this leave the tribunal? In somewhat difficult and uncharted territory, it would seem. So what does it do next?

Judge Moriarty has not said he is going to be altering his provisional findings, but it seems impossible for him to now say that the licence was issued in the face of concerns about its legality – something everybody believes it was poised to say until the latest evidence.

The tribunal looks trapped between a rock and a hard place. It has given parties three weeks to respond to the latest evidence but this is likely to be overtaken by events.

There are, of course, other serious potential findings – for example, issues concerning the actual licence competition process, as well as possible financial links between O'Brien and Michael Lowry – that wouldn't appear to be directly affected by the evidence of recent weeks.

But with the tribunal's vulnerability now so exposed, it seems inevitable that some of the affected parties will now seek to closely scrutinise the other potential findings for weaknesses. Further legal challenges to the tribunal look a distinct possibility and maybe even a probability.

"This isn't over. Not by a long shot," one close observer said last week. The once unthinkable prospect of the tribunal 'celebrating' – if that's the right word – its 13th birthday in the autumn suddenly looks far from unthinkable. Unlucky 13, it would seem, not least for the hard-pressed taxpayer.