The High Court has reserved its decision on whether United Left Alliance TD Joan Collins should have to pay the costs of her failed challenge to the issuing of €31 billion worth of promissory notes.

Ms Collins's case was rejected by a three-judge division of the High Court last November.

Normally, the unsuccessful party in a court action must pay the costs.

But Ms Collins' lawyers argued that because she had raised issues of exceptional public importance, she should not be liable for the costs.

Ms Collins had argued that it was unlawful and unconstitutional for the Government to disperse such massive amounts of money out of the central fund without Dáil approval.

The issues in her case were described by the court as "weighty" and important and had not been litigated before.

Senior Counsel Michael McDowell, for the State, said there was a difference between a case raising important issues and whether or not it was in the public interest to bring such a challenge.

He said in view of the fact that Ms Collins was pursuing an appeal to the Supreme Court, he had been instructed to apply for the State's costs.

The three judges said they would reserve their decision until a later date.