Minister for Finance Michael Noonan has told the Dail the mistake in the national accounts of €3.6bn was "human error" on behalf of an official in the Department of Finance.

He was responding to a question raised by Fianna Fáil's Michael McGrath.

Mr McGrath described the miscalculation of the national debt as “a humiliating schoolboy error”.

He explained in the Dáil that the double count arose because the Housing Finance Agency had borrowed directly from the NTMA instead of from the open market in 2010.

He explained that general government debt is compiled by adding the central government debt borrowed by the NTMA to debt sourced on the open market by government bodies.

However, he said, when the HFA borrowed from the NTMA, the €3.6bn in question was already in the central government debt figure.

As the liabilities of the HFA were then added to the general government debt figure, the €3.6bn was counted twice.

Mr Noonan said the NTMA also had questions to answer. He called for external investigation into the matter.

Mr Noonan said it was clear there had been a systems failure and said it was a very serious issue.

He said the Secretary General of the Department of Finance had been asked to conduct a review into the matter.

He also said the CSO had already informed Eurostat of the double count and the EU and IMF have also been informed.

Ireland was in no way better off following the discovery of the accountancy error, he said.

Elsewhere, the Public Accounts Committee will hold a special session tomorrow to discuss the error in the national accounts that came to light yesterday.

The correction has reduced the national debt by 2.3% but will not have any impact on next month's Budget.

Department of Finance accounting officer Kevin Cardiff and senior officials from the CSO and the National Treasury Management Agency will be questioned tomorrow morning by the committee, which is anxious to get details of just how the error happened.

PAC Chairman John McGuinness said that as well as dealing with the error, and on when it came to light, the committee will also examine the control failures that led to its happening.

The committee will meet at 10.30am tomorrow.