Irish Nationwide had a special bank account called the 'No. 3 account' which was used to immediately disburse funds when required for sensitive situations.
The account was jointly controlled by Michael Fingleton, the building society's boss, and just one other member of staff between 2002 and 2008. It could make payments without formal limits and was used for purposes including granting loans to politically sensitive figures or for the settlement of disputes.
The existence of this unorthodox bank account was one of many unusual practices identified by forensic accountants from Ernst & Young, who were asked to trawl through the society by the State, post the bank guarantee.
Ernst & Young also identified issues relating to individual borrowers that it considered unusual, including loans to some of the society's biggest borrowers.
These and many other issues are revealed in a new book called Fingers, by Tom Lyons and Richard Curran, which is to be published by Gill & McMillan next week.
This book identifies a range of unusual deals, including a payment of €435,000 to a firm which the society's records say has an address on Madison Avenue, New York.
Ernst & Young was unable to find any evidence of this company at that address and concludes that the beneficiary of this payment is a Luxembourg bank account.
It also identifies multimillion sums being paid out for "consultancy services" to entities related to some of the society's borrowers. It also lists a range of other payments sanctioned by Fingleton that Ernst & Young found required further questioning.
The book reports on other shortcomings of the society, identified in April 2009 by consultants Deloitte. These include the fact that not all commercial loans were subject to review by the credit risk department; adherence to the credit committee's terms of reference were not always met and the society stopped producing quarterly reporting packs on credit-risk management in September 2007.
Deloitte found that terms were extended on certain loans in December 2008 without borrowers requesting it. Fingers also identifies various donations to political parties and gifts to members of staff as among the lavish spending by the society in its final years before it collapsed at a cost to the taxpayer of €5.4bn.
The vast array of unorthodox and/or bizarre practices that went on inside Irish Nationwide are the subject of two separate investigations.
The first by the Central Bank into lending practices in the society has been ongoing for two years. The second initiated by IBRC, which took over the society in 2012, is also ongoing despite the bank being placed into liquidation. KPMG, the special liquidator of IBRC, is currently reviewing this second case.
IBRC's special liquidator has until the end of this March to decide on what grounds it will or will not proceed with any action against Fingleton and other former board members of the society. Fingleton did not return calls for comment on Friday.