Big Four accountancy group EY and corporate law firms Arthur Cox and Mason Hayes & Curran have emerged as the biggest fee-earners from 15 years of regulatory investigations and an inquiry into Irish Nationwide Building Society (INBS) that cost the Central Bank €24.3 million.

EY earned €4.29 million for acting as forensic accountants and assisting an investigation team from the Central Bank as it went about building up an investigation report between 2010 and 2015, when the regulator decided to send five former senior INBS figures forward for a public inquiry.

The breakdown of costs was disclosed on Wednesday as the inquiry drew to a close with the publication of a decision that the last of five men subject to the inquiry, INBS’s one-time finance director John Stanley Purcell, be disqualified for four years from managing an financial firm and fined €130,000.

Arthur Cox, the third-largest law firm in the State by solicitor numbers, secured €3.35 million in fees between 2016 and this year assisting the three-member panel that presided over the long-running inquiry.

Mason Hayes & Curran, the fourth-largest law firm, drew in €2.44 million over the past decade as legal advisers to the Central Bank and its enforcement division during the course of the inquiry. This included work MHC carried out between 2015 and 2018 as Mr Purcell and INBS’s former managing director, Michael Fingleton, pursued a legal challenge against the inquiry. That challenge ultimately failed.

Accountancy firm Grant Thornton was also among the top-earning organisations, generating €2.15 million of fees for its role in providing data management and other services between initial inquiry hearings that started in private in 2016, public hearings that ran over 105 days between 2017 and 2021, and subsequent work by the inquiry team.

The highest-earning individual lawyer was Brian O’Moore who received €1.51 million as a legal adviser to the inquiry panel between 2015 and 2019, when he was a barrister. He was subsequently appointed a High Court judge in 2019 and became a judge of the Court of Appeal in 2023.

The chair of the inquiry panel, solicitor Marian Shanley, received €1.36 million in fees and expenses, while the other two panel members, Geoffrey McEnery and Ciara McGoldrick received €1.23 million and almost €557,000, respectively.

“The costs of the investigation and inquiry reflect its length (15 years) and complexity, including the extensive work to unearth the facts through a large volume of documentation and witness evidence, and the need to defend the statutory framework in the face of court challenges by persons under inquiry,” said Central Bank governor Gabriel Makhlouf.

“The lessons learnt have led to changes to the legislative framework, which have introduced efficiencies and further safeguards.”