A High Court action being taken by former Labour Party TD Joe Costello seeking to increase the number of members in the next Dáil has little chance of delaying a general election, legal sources believe.

In his case, which will be heard on Tuesday by Mr Justice Peter Kelly, Mr Costello will argue that before any election is called the Government must increase the number of TDs by one to reflect the increase in the population shown in the last census.

Mr Costello has a personal interest in seeking such a declaration in that his own Dublin Central consistency would gain the extra seat, significantly increasing his election chances.

Article 16.2.2 of the Constitution states the total number of members of Dáil Éireann “shall not be fixed at less than one member for each thirty thousand of the population or at more than one member for each twenty thousand of the population”.

The 2016 census shows Dublin Central should have four TDs instead of three. However, legal observers note the courts are extremely reluctant to involve themselves in electoral affairs and that judges have no power to tell a Taoiseach when he can dissolve the Dáil.

The timing of the challenge has the potential to raise a number of unprecedented legal scenarios.

‘Allergic’ courts

The first scenario is the most likely – Mr Costello loses his case and the Taoiseach is free to proceed to a general election if he wishes. Senior lecturer in constitutional law in UCC Conor O’Mahony points out that similar challenges have failed in the past and the courts are “nearly allergic” to getting involved in electoral matters.

He said there is “no question” the current number of seats in Dublin Central is a breach of the Constitution. “The big question is what the courts can do about it in this timescale. And there doesn’t seem to be much they can do.”

The second scenario sees Mr Costello winning the case and the court declaring the law must be changed before an election.

Mr Costello, unlike those taking previous challenges, is seeking relief under article 16.2.2 of the Constitution which states “in black and white” the number of TDs there has to be per person, according to Mr O’Mahony. Therefore the court might be forced to issue the declaration that the current system is unconstitutional. This would trigger an immediate appeal by the State but it would also make it a lot harder for the Government to call an election.

Confidence vote

Scenario three is the most interesting and the most disruptive. If the Government collapsed on Tuesday after losing a confidence vote, a situation might arise shortly afterwards – perhaps on Wednesday morning – when the High Court sided with Mr Costello and declared the current electoral system unconstitutional.

This raises the prospect of the Dáil being unable to pass remedial legislation – having just been dissolved – but with no election able to take place until such legislation is passed.

“When you draft a Constitution you try to think of everything but these are the quirky things that can arise. It’s the kind of thing us constitutional lawyers love,” said Mr O’Mahony.