The highest court in the European Union has ordered the European Commission to re-open an investigation into the Irish travel tax.

The European Court of Justice has annulled a previous decision - meaning another inquiry will be held into whether the tax was a form of illegal state aid.

The case was taken by Ryanair, who claimed that internal flights run by Aer Arann and Aer Lingus were the only ones that could benefit from a lower rate of travel tax.

It complained to the European Commission which dismissed the complaint three years ago, but now a new inquiry will have to be held.

The travel tax stood at €10 for most flights, but only €2 for shorter ones. However it was reformed in 2011 and abolished altogether in April of this year.

Ryanair have welcomed the ruling.