One of Ireland's leading constitutional lawyers has said Taoiseach Enda Kenny will be required to formally resign as Taoiseach if he fails to win majority support in the Dáil on Thursday.

Former attorney general John Rogers said a precedent was set in 1989 when the then Taoiseach Charles Haughey had to resign but stayed on as caretaker Taoiseach until a government was eventually formed and elected by the Dáil.

He said article 28 of the Constitution was very clear and he believes this would apply if the same happened later this week.

Speaking on Newstalk’s Sunday Show, Mr Rogers said that there were “some attempts” to form a government at the time but “a little bit like now, one got the impression that some people really didn’t want to be in government.”

"There would have been a view at the time that Fianna Fáil and Fine Gael ought to get together at that time."

Mr Rogers said one obstacle to such an agreement being reached would have been the prospect of Labour Party leader Dick Spring becoming leader of the Opposition.

“Of course one of the problems with that from the perspective of some of the other parties would have been that Mr Spring would become leader of the Opposition. You’re getting a sort of replay of that now,” he said.

He recalled how he met Mr Spring and Mr Brendan Howlin on the morning the Dáil was due to convene.

“We discussed what would happen and I was very exercised by Article 28 (of the Constitution) and what was the effect of it. I took the view that a Taoiseach who had lost a vote in the Dáil was obliged to resign by placing his resignation in the hands of the President.”

He said the Constitution provides for “the outgoing Taoiseach and Ministers to remain in their offices although they have resigned, in a sort of acting capacity”.

He recalled how “before I left though Brendan had gone down through the House somewhere and when he came back he said he had met PJ Mara and he said ‘well will you be resigning, later’ and PJ Mara had said ‘not at all. No’.

He said “so that had confirmed to us perhaps this was the tack the government was about to take”.

He was "away all day and much later I rang Leinster House and a woman answered the phone and said Dick Spring had just forced Charlie Haughey to resign.

That’s my memory of it and that’s what happened. The world didn’t fall apart but a Constitutional principle was established. The democratic form of the Constitution was reinforced I think.”

He believed that on Thursday next the President would request Taoiseach Enda Kenny to stay on.

“In ‘89 there was a lot of talk during the day between the Taoiseach’s advisors and other leading members of Leinster House, the parliamentary parties, and Mr Haughey did resign and that resolved the issue.”

He felt “that’s the appropriate way it should be resolved. My view is that it is a very important signal that the Constitution is effective”.

He believed that if the Taoiseach doesn’t secure a majority vote in the Dáil on Thursday “that’s what should happen.”

He added “you could say there was a political precedent for it. I don’t know what’s now written down anywhere. It may be that some of the logs in the Attorney General’s office contain some guidance on it and it’ll be by that I imagine that Enda Kenny would be advised but the reality is that he was there at the time in ‘89 and I don’t see this position being contradicted and frankly I think it would be a very bad day if it were, as Article 28 is very clear in my view.”

Meanwhile, former taoiseach Bertie Ahern has said speculation about the likelihood of a Fianna Fáil/Fine Gael government is premature as many other political combinations would have to be considered first.

“I think the more talk there is that this might happen next Thursday or Friday or Saturday, then it won’t happen,” he told Newstalk’s Shane Coleman on Sunday.

“Nobody will want an election this year,” he said.

Considering the likely make-up of the next government Mr Ahern said “you could go through the list and maybe a combination would work and maybe then you’ll have to go to the back of the page, the back of the page would be Fianna Fáil/Fine Gael. You’d have to go down through the list first,” he said.

Views on the shape of the next government will change, he said.

“There’ll be opinion polls, public opinion will have changed. That’ll all have evolved over the next three or four weeks. It’s the way it always happens,” he said.

He also said that Fianna Fáil leader Micheál Martin will seek the office of taoiseach on Thursday “because the day you go in to play a match to lose is a bad day. Micheál Martin will be going in to win and he should.”