The question is obvious and voters in Northern Ireland have a right to an answer before they go to the polls on December 12th. What will Sinn Féin do if the election results in a hung parliament? More specifically, what will it do if its votes could make Jeremy Corbyn prime minister and he makes the party an offer it surely can’t refuse?

The offer is this: take your seats to vote me into office and support me on any confidence motions, and in return I will give you a Border poll. Does Sinn Féin really rule out such a deal? And if not, it surely needs to be honest with voters and prepare them in advance for the possibility that the policy of abstentionism is not as absolute as party dogma has always claimed it to be.

I know, of course, what Sinn Féin’s immediate answer to the question will be: we don’t do hypotheticals. But everything about UK politics is hypothetical right now. Every objective observer accepts that the electorate is more volatile than it has been for generations.

Corbyn is effectively a Sinn Féin fellow traveller. During the 1980s and 1990s he was the closest thing the party had to a sitting MP In 2017 the Conservatives and Labour got 83 per cent of the vote between them – the highest combined total since 1970. In this year’s European Parliament election, they got 23 per cent between them – the lowest total in the era of mass democracy. A binary first-past-the-post system now has four major parties squeezing into it. Small shifts could produce momentous results. Nobody knows how many voters will decide to vote tactically. Nobody knows anything.

A guess that is as good (and as bad) as anyone else’s is that Boris Johnson either wins big or not at all. He is gambling everything on one throw of the dice: that “get Brexit done” will deliver a slew of Labour seats in the coastal towns, the midlands and the north of England, easily offsetting his likely losses in Scotland, the southwest and London. The likelihood is that if this gamble pays off, it will be a jackpot – those Labour seats, if they fall at all, will fall like dominoes. But if they don’t, what then? Related Fintan O'Toole: Ireland's young and working classes are in the Covid-19 firing line

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Doing deals What then is that if Corbyn is to have any chance of forming a government, he will have to do deals. One big deal will be with the Scottish National Party: the price will be a new referendum on independence for Scotland. But he will need others.

An option – utterly bizarre but by no means beyond the very wide bounds of current possibilities – would be a deal with the DUP. (Weird as it seems, a Corbyn offer to renegotiate the withdrawal agreement and stay in the single market and customs union – thus removing the threat of a “border in the Irish Sea” – could be the DUP’s last ladder out of the hole it has dug for itself.)

But Corbyn is effectively a Sinn Féin fellow traveller. During the 1980s and 1990s he was the closest thing the party had to a sitting MP. He opposed the Anglo-Irish Agreement of 1986 on Sinn Féin’s party line that it must be a united Ireland or nothing. He has never unequivocally condemned the IRA’s murder campaign.

Clearly he would be much more comfortable relying on the support of those to whom he has been so close for so long. And he just might be in a position to make a bold offer: put me into 10 Downing Street and I will give you a Border poll in 2020. The date, of course, is resonant: it will be 100 years since the Government of Ireland Act partitioned Ireland.

This is a welcome concession to political reality, but it also creates a very strange logic An important consideration here is that Sinn Féin has already in effect shifted its position on abstentionism. Last week the party announced it would not stand in South Belfast, East Belfast and North Down and urged its voters in those constituencies to support Remain candidates instead.

Strange logic This is a welcome concession to political reality, but it also creates a very strange logic. In calling on voters in three constituencies to vote for candidates who would in fact take their seats, Sinn Féin is saying that what happens in Westminster after the election is of vital interest to those voters.

In those three constituencies, the party is saying Brexit trumps everything else and every seat in the House of Commons may be crucial. But not, apparently, in the other 15 constituencies, where voters are expected to support Sinn Féin candidates who will then do nothing with their seats. This makes no sense whatsoever. It amounts to abstentionism for some voters and non-abstentionism-by-proxy for others.