Green Party leader Eamon Ryan should be taoiseach for one year of a five-year coalition between Fianna Fáil, Fine Gael and the Greens, senior figures in that party have said.

Fine Gael has repeatedly said its party, if it enters into coalition with Fianna Fáil, will require the taoiseach’s position to be rotated between Fianna Fáil leader Micheál Martin and Fine Gael’s Leo Varadkar.

Mr Martin this week confirmed he would go into government with Fine Gael, subject to agreement on policies, and did not rule out rotating the office of taoiseach. Fine Gael’s position is that it wants to go into opposition, but has not ruled out entering government with Fianna Fáil as a last resort.

Although government-formation talks have yet to make any substantial progress, a Fianna Fáil/Fine Gael/Green Party coalition, including some Independents, is seen as the most serious option at this point.

However, senior figures in the Greens propose that the position of taoiseach be split between the three parties over a five-year term, with the leaders of the two so-called Civil War parties getting two years each and Mr Ryan getting one.

“Mathematically it makes sense,” said a senior Green source. “2-2-1.”

Debate is continuing within the parties about the merits of such a coalition after Mr Martin faced calls this week from some within his parliamentary party to open talks with Sinn Féin.

A new grassroots group in Fianna Fáil has organised to oppose moves to form a coalition between the party and Fine Gael, and is lobbying TDs to speak up at parliamentary party level.

In a further sign of potential difficulties, Mr Martin was robustly criticised by Galway West TD Hildegarde Naughton at the Fine Gael parliamentary party meeting this week. Ms Naughton claimed Mr Martin’s health policies, particularly on providing hospital beds, raised “red flags” and serious concerns.