IT could could take 10 years to resolve the €14.3bn Apple State aid battle between the European Commission, Ireland and the tech giant, the Public Accounts Committee has been told.
Following a two-year probe, the Commission ruled in 2016 that Apple had benefited from illegal State aid totalling €13.1bn.
The case is the biggest illegal State aid ruling ever by the European Commission.
Challenging it has already cost the State €7.1m, the Committee heard. Last year, the tech giant transferred the disputed €13.1bn-plus interest of €1.2bn to Ireland, with the money being held in escrow.
Apple and Ireland are appealing the State aid allegations, arguing that Apple never benefited from illegal aid.
The funds will be held in escrow until such time as the appeals are completed.
The Government last year appointed BNY Mellon to manage the Apple escrow account.
European Commissioner for Competition Margrethe Vestager - tipped to be the Commission's next president - said in 2016 that "Apple's tax benefits in Ireland are illegal" and reliefs granted to the company by Ireland had "artificially reduced Apple's tax burden". But it could now take years before there's a final outcome from the appeal.
Derek Moran, secretary general of the Department of Finance, said: "This could take many years. We had an expectation of having a preliminary hearing this side of the summer, but that hasn't happened.
"In my experience, by the time this gets through the full process of litigation, up to and including the ECJ [European Court of Justice], this will probably be several years," he added.
Asked by Fine Gael TD Peter Burke, who's a member of the Public Accounts Committee, if it could be a decade before it's resolved, Mr Moran said he is aware of a separate case that has been running for longer than that.
"I certainly know of one State aid case that is significantly more than a decade," he said.
That relates to another State aid case taken against Ireland by the Commission in relation to the Aughinish Alumina plant on the Shannon.
Mr Moran said the State has already paid €7.1m in costs in relation to the Apple case. That includes €3.7m on establishing an escrow fund for the Apple cash. An additional €3.4m has been paid in legal fees.
Mr Moran said that €90,000 has also been paid in translation costs, while there had been €65,000 in other costs.
He added that at this stage the Department of Finance does not have a "fixed projection" in the likely ultimate legal and other costs.
But he said the final legal cost to the State has "the potential to be significantly more" than the €3.4m already incurred.
Europe's second-highest court will rule tomorrow whether a Belgian tax break which benefited some 35 large companies is illegal state aid, a judgment which could provide clues to other tax cases involving Apple, Starbucks and Fiat Chrysler.