Competing legal opinions have been put forward as to the constitutionality of the Seanad sitting without all 60 members as protracted government formation talks continue.

The debate has intensified because of the approaching deadline to renew the legislation underpinning the operation of the non-jury Special Criminal Court, which is typically renewed every summer.

A group of Labour and Independent Senators, including two respected lawyers, Labour Senator Ivana Bacik and Independent Senator Michael McDowell, have told the Taoiseach they will seek a court judgment on the matter, The Irish Times reports.

In a letter to the Taoiseach, they said: “We intend to apply to the High Court for a speedy, authoritative and binding determination by way of declaration on this important issue of constitutional interpretation unless it is clarified that you share our understanding on this issue and consider yourself constitutionally free to advise the President to fix a day for the first meeting of the newly elected Seanad in early course.

“Unless we receive this clarification it would be our intention to issue and serve a plenary summons and deliver a short statement of claim seeking the appropriate declaration, naming you as defendant and making the Attorney General a notice party.”