Stephen Donnelly, the energetic Independent TD for Wicklow and east Carlow, is generally credited with having struck a severe blow to the credibility of the forthcoming banking inquiry. Five weeks ago he resigned from the inquiry claiming the Taoiseach had subverted it by making sure the Government had a majority on the committee.

The inquiry has struggled on gamely without him, but its credibility was dealt a fatal blow last week by Public Accounts Committee (PAC) chairman John McGuinness. It emerged last last week that McGuinness had privately met former Rehab chief executive Angela Kerins and her public-relations adviser before her appearance in front of his committee last February.

According to Kerins, McGuinness advised her about the hearing and said the committee understood the limits of its powers. He also appeared to hold himself out as some sort of honest broker, warning her that members of the committee did not like her. More damagingly, Kerins, in a High Court affidavit, said McGuinness had previously raised with her the case of former Rehab executive Pat Fitzpatrick, now a Fianna Fáil councillor, who was losing his job as chief of a Kilkenny unit of the organisation.

McGuinness defended his actions – which surprised some of his fellow committee members – saying there was nothing unusual in this and that he had met Kerins as he would any witness “and I outlined the procedures as to what would be expected of her as a witness”.

Kerins is arguably not just any witness. She was the most controversial witness to appears before the PAC in years and also a well-known figure in Fianna Fáil, the political party to which Mr McGuinness belongs. She had sought a place on its national executive and chaired the Women's Political Association. She was appointed to so many State boards that she earned the sobriquet "the quango queen".

Tribune of the people

McGuinness’s response gives a insight into how the PAC operates and what its real agenda is. If, as we are led to believe, the PAC is some sort of tribune of the people that calls the powerful before it and fearlessly holds them to account on behalf of the taxpayer, it is hard to see what business its chairman has meeting an important witness ahead of time and telling them what to expect. It is even harder to understand why he would do it without telling the other PAC members.

McGuinness’s actions paint the PAC in a rather less flattering light. It makes it look like the committee’s main purpose is to make the members look good and allow them advance their own agendas.

The reason that McGuinness’s actions are so damaging for the credibility of the banking inquiry is that the inquiry is really the PAC on steroids. It harks back to the glory days of the PAC in 1999 when the Dirt inquiry ran roughshod over bankers, to the delight of the public.

That inquiry was, in truth, a bit of a farce. It found nothing that had not already been established by a comprehensive investigation by the comptroller and auditor general. It did at least hold some of the actors to account in public, but only some. The chief executives of the banks got a good going over but various ministers for finance – whom the C&AG had shown had knowledge of what was going on – all got off scot-free. It was pretty much what you would expect from an inquiry run by politicians.

Lionised by media

However, the publicity and prestige enjoyed by the PAC members – including those who held undisclosed offshore bank accounts – was unprecedented. They were lionised by the media. They wanted more; and further inquiries were planned.

It was brief and glorious awakening. The courts quickly pointed out that they – rather than gangs of publicity-crazed politicians – were the people charged with establishing facts and dispensing justice.

The political class has mourned the neutering of the PAC ever since and has made many efforts – including an ill-fated referendum in 2011 – to try to find a way to get its hands on such powers again.

The banking inquiry is the first outing of the compromise that emerged after the people chose not to give them what they wanted. McGuinness has shown them they were wise not to trust politicians to investigate politicians and political acts. The banking inquiry, sadly, will be further proof.