To the grassroots members of each party, the prospect of a Fine Gael-Fianna Fáil coalition is as disconcerting a notion as an amalgamation of Celtic and Rangers football clubs would be in Scotland.

Yet the call to end Civil War politics is almost as ancient as the divisions that led to the creation of the two parties. Prof Gary Murphy of DCU has written about an approach by Fine Gael to Éamon de Valera ahead of the 1957 elections to form an alliance. The Fianna Fáil president Seán T O’Kelly consistently spoke of the need for “reconciliation” between the parties in the late 1950s. In the 1970s, Fine Gael’s John Kelly and Fianna Fáil’s Charlie McCreevy argued separately that there was no longer a basis for the historical difference between the parties.

The idea never took hold, but the notion of a “grand alliance” has re-emerged since the 2011 elections. It is discussed not because of any ideological change but because of mathematics. A partial recovery by Fianna Fáil, a weaker performance by Fine Gael and a precipitous fall for Labour in the next election would place the two biggest parties under enormous pressure to form a government.

For both parties, the prospect might be marginally more attractive than dealing with Sinn Féin, with a variety of independents and splinter parties, or with a damaged Labour.

The idea was given further impetus by former Fianna Fáil TD Mary O’Rourke at the Carleton Summer School in Co Tyrone earlier this month. “I am . . . inspired by what has been able to be done in Northern Ireland, of the differences which have been overcome and accommodated. Is it not time to bury the totem poles and fly the common flag of Michael Collins and Éamon de Valera?”

Sports presenter and Fine Gael strategist Bill O’Herlihy has also made it a theme of the speech he will deliver at the annual Michael Collins commemoration at Béal na mBláth in west Cork tomorrow.

But are the parties really so close? “It’s too easy and facile to say they are the same because of matching economic policy,” says Prof Murphy. The parties have historically differed: on the economic war with Britain; on the national question; on the Irish language and culture; and the role of the State in industry. Different social strata have been drawn to each party. Fine Gael has been seen as more principled, Fianna Fáil as more pragmatic, sometimes even to the point of corruption.

Fine Gael’s Brian Hayes agrees: “There is a value difference. Fine Gael is more liberal. Fianna Fáil is more conservative but more pragmatic.”

Labour’s Emmet Stagg, who was in government with both parties, puts it more bluntly. “Fianna Fáil ministers agreed with everything. Fine Gael ministers argued about everything.”

From a purely political perspective, members of both parties would resist it. Hayes says the absolute strategic objective for Fine Gael is a second term with Labour. “We are haunted by 1997 and the election where Bertie Ahern led Fianna Fáil into power for 14 years. It’s important for the country to get a break from Fianna Fáil for at least a decade.”

Fianna Fáil’s Michael McGrath believes that the electorate will not be ready to forgive his party in 2016, and that government is not an option until 2020 at least. He agrees they are close to Fine Gael on some issues but says the distinctions are more marked than is the common perception. Fianna Fáil is a left-of-centre party now, he says, while Fine Gael is well to the right. For him, the dominant issue in the election will be economic management, and it will be critical for Fianna Fáil to carve out its own space on economic policy.

Being a minor partner in a coalition is risky, given how the electorate has punished smaller parties in the past. “It is exceptionally difficult for a smaller party to retain a distinctive identity in government. That holds true for the current coalition even though Labour won close to 40 seats,” says McGrath.

If Fianna Fáil were damaged by such an alliance, this could create an electoral opportunity for Sinn Féin. “Sinn Féin poses a significant risk in terms of FF’s self-interest, but we cannot allow ourselves to be motivated by that,” says McGrath.

The arrangement would be welcomed by other parties, however. “I have long argued that the political choice should be between left and right,” says Stagg. “I still believe that strongly as it would normalise politics.” Sinn Féin’s Pearse Doherty also argues for realignment. “The left have to come together too. It should be based on values and not something historical.”

The political blogger and Fine Gael member Dan Sullivan also points to some other unpredictable consequences of an FG-FF alliance. “I actually think the mistrust between both parties would be much higher. We perceive Fianna Fáil as wide boys who play fast and loose with the rules, while they see us as ‘big house’, superior and condescending.”

He also argues that you need stable opposition as well as stable government. “If support for both parties fell, it does not follow that Sinn Féin and Labour would pick up all the votes. You could see tiny new parties, far more independents, continuity parties, rumps of parties. It could lead to huge instability.”

Murphy, McGrath and Hayes separately identify stability as the biggest benefit of a political system dominated by parties of a similar hue. Murphy contends that a single opposition party has always offered a moderate, non-radical, alternative government.

Says Hayes: “Peter Barry [a former Fine Gael deputy leader] said to me that the long-term viability of Fine Gael is based on the long term viability of Fianna Fáil. What he meant was that both offer government that effects non-radical change. They have offered modest change and long-term stability. We are the third-longest continuous democracy in Europe.”

To return to the soccer metaphor: this is also a little similar to Celtic and Rangers. Bitter rivals as they are, Scottish football is at its strongest when both are strong.