Court rules State cannot claim privilege over travel tax documents being sought by Ryanair and Aer Lingus

The airlines are also seeking damages from the State over what they say was the unlawful levying of a variable rate tax between 2009 and 2011.

In December 2016, as part of the process leading up to the hearing of the actions, Mr Justice Max Barrett ruled the State was entitled to claim litigation privilege over documents deployed when the State defended proceedings brought against it by the European Commission over the tax.

Following a decision from the Commission, the tax of €2 for flights under 300km and €10 for those over 300km, was reduced to a flat rate of €3.

In April 2014, the rate was cut to zero.

Mr Justice Gerard Hogan, on behalf of the three-judge appeal court, said there is no doubt the pending High Court proceedings by the airlines traverse similar grounds to those involving the European Commission.

Mr Justice Barrett, in his decision, said the airlines' case involved "closely related litigation".

Mr Justice Hogan said he differed from the High Court judge in that respect because the parties, in this case, are entirely different and there was no direct linkage between the now concluded Commission proceedings and the present litigation.

Accordingly, he said, the "zone of privacy" which the State required to defend the Commission proceedings, and which gave rise to the litigation privilege in the first place, is no longer required now that those proceedings are over.

It must, therefore, be concluded that because those (Commission) proceedings have ended, the State cannot claim litigation privilege over the documents.

It may be the State will be able to assert legal professional privilege over some or all of the documents, or claim public interest privilege, but those are arguments for another day, he said.