The Government's auditor has calculated that both the cost of compensating victims of residential abuse and the €127 million contribution from religious bodies were under-estimated.
In his report, John Purcell says the deal might cost €1 billion, a figure disputed by the Minister responsible, Dr Michael Woods.
The review was undertaken by the Comptroller and Auditor General at the request of the Oireachtas Public Accounts Committee. Over 29 pages, John Purcell examines both the causes - and the consequences for the taxpayer - of the controversial child abuse deal of June last year.
In the deal 18 Catholic orders agreed that Michael Woods - and his successors in government over six years - would pay the entire bill when former residents of more than 80 Church-run institutions won damages in the Courts.
The State's financial watchdog estimates the maximum cost of the deal as follows:
He says 10,800 former residents may claim compensation and may get €96,600 on average, leaving the State to pay out €1 billion.
To help defray this, the religious groups promised to give a total of €127 million in cash and kind. This works out at one eighth of the total cost.
Michael Woods has disputed what he called the watchdog's billion euro 'guesstimate', saying John Purcell was 'probably wrong'.
John Purcell says negotiations between church and state almost broke down in late 2001, prompting Dr Woods to personally take charge of them and to cap the orders' contributions at €127 million.
But he implies Dr Woods could have demanded €190 million from the religious if he had used his department's own up-to-date estimate of the spiralling number of people expected to claim compensation.
The report notes that the former Attorney General, Michael McDowell, was not represented at - or informed about - meetings between government representatives and religious congregations for six months after Michael Woods took personal control.
Before the deal was signed - in the final week of the last Coalition's life - Mr McDowell pointed out that the religious orders' contribution might be regarded as insufficient and highlighted the lack of a mechanism for increasing it if the numbers of compensation cases increased greatly.
