Sensitive material relating to the €158 million Mahon Tribunal, which prompted the resignation of former taoiseach Bertie Ahern from Fianna Fáil, is set to be locked away for 30 years as the inquiry is finally dissolved.

Chairman Mr Justice Alan Mahon is soon expected to formally confirm to Government the completion of his work after tribunal personnel contacted the Department of the Environment in recent weeks.

A spokesman for minister Alan Kelly said: "Tribunal officials have communicated to the Department of the Environment that they feel their work is complete. It is expected Mr Justice Alan Mahon will write to the Minister to formally communicate that shortly."

The tribunal was set up in 1997 to look into alleged corruption in planning.

Third parties who engaged with the tribunal will now have documentation, thought to include maps and bank account details, returned. All remaining information will be handed over to Mr Kelly.

Private interviews

Under the National Archives Act, the material may be published three decades after the tribunal’s dissolution. It is believed to include interviews and internal briefing documents.

Public hearings were completed and a final report published in 2012. However, in January it emerged the tribunal had to withdraw large portions of two earlier reports after losing a number of court cases.

The State became liable for the legal costs of some individuals after findings of planning corruption and obstruction were set aside. Some findings made against former Fianna Fáil minister Ray Burke and others were withdrawn.

The withdrawal of the findings based on the evidence of the tribunal's star witness in its early days, the late James Gogarty, means years of work at the tribunal were largely wasted.

However, adverse findings against prominent individuals in a number of its interim reports still stand, and nothing in the final report, on Mr Ahern’s finances, was withdrawn.