Leo Varadkar says he would resign from Fine Gael rather than go into coalition with Sinn Féin

However his predecessor, current Tánaiste Micheál Martin, has refused to rule out going into government with Sinn Féin.

Speaking on Two Tribes, the RTÉ documentary by broadcaster Sean O’Rourke, Mr Varadkar said he would be “totally against” Fine Gael going into government with Sinn Féin.

“I’d be totally against it, could not lead my party into a coalition with Sinn Féin.

“I’d resign as a member,” he said.

However Mr Martin did not rule out a coalition with Mary Lou McDonald’s party.

“I think economically and politically, there would be huge difficulty in going into government with Sinn Féin,” said Mr Martin.

“I would say in the next general election, ruling out parties may not be as strong…in other words, we’ll leave it to the people to decide.”

Fianna Fáil senator and Seanad leader Lisa Chambers also echoed his comments, saying the party could not rule out going into government with Sinn Féin.

“A lot of our members can remember the Troubles and I think would be quite upset, actually, at the prospect of that,” she said.

“But I suppose from my own perspective, being honest about it, I don’t think it’s something that we can ultimately rule out.”

Meanwhile Sinn Féin leader Mary Lou McDonald said she would talk to any party about government formation.

“I’ll speak to everybody,” she said. “I think that’s what grown ups do. I think that’s the adult and in fact, the respectful thing to do.”

On the same programme, the Taoiseach admitted how he got “wrong” a coup in 2010 against then Fine Gael leader Enda Kenny.

Mr Kenny won a motion of confidence in his leadership of Fine Gael, which put an abrupt end to an unexpected and dramatic attempt by his deputy leader Richard Bruton to unseat him.

Mr Varadkar, who was a new TD at the time, backed Mr Bruton on RTÉ’s Primetime.

He remained a frontbencher but was moved to a different portfolio.

Mr O’Rourke pointed out how Mr Varadkar with “barely three years in the Dáil” and was trying to force out his party leader.

"I got that one wrong, didn’t I,” said the Taoiseach.