The 18 parliamentary seats in Northern Ireland are normally treated as a bit of an afterthought at a general election. They are not contested by any of the main British political parties, and are always the last to declare, their results tending to trickle in long after the polls are closed and when the identity of the new government is already known.

But those 18 seats may become a whole lot more consequential in 2015 if there is a hung parliament (which is very likely) where no two parties are able to agree on forming a coalition (which seems increasingly likely).

It could then be the case that Northern Ireland’s MPs turn from courtiers to kingmakers, and a tiny number of seats take on a huge significance.

This is how things stand currently:

Sinn Fein by tradition does not take its seats in the Commons, meaning the maximum number of MPs in the present parliament is 645 rather than 650. This also means the unofficial figure needed for an absolute majority in the Commons is 323 rather than the official number of 326, and would be again in the next parliament, were Sinn Fein to hold on to all its seats and once more decline to attend.

Such a distinction is just the sort of detail that would loom awfully large in the minds of David Cameron and Ed Miliband were they faced with the task of governing as a minority party in a hung parliament. It has also been looming large in the minds of Sinn Fein, according to certain reports. Might the party reverse its position and take its seats if it meant helping to prevent, say, a Tory-DUP coalition?

An added twist is that one of Sinn Fein’s five seats is the narrowest marginal in the entire United Kingdom: Fermanagh & South Tyrone, won in 2010 by Michelle Gildernew by a majority of just four:

Here’s where things stand getting rather intricate.

The Ulster Unionists, who currently have no MPs, have proposed a pact with the DUP in Fermanagh & South Tyrone. Its leader Mike Nesbitt has suggested the DUP does not field a candidate in the seat and instead pledges support for the UU candidate. Nesbitt’s obvious intention is to avoid splitting the unionist vote and maybe win the seat, in the process getting the Ulster Unionists back into parliament.

In return he is proposing a second pact in Belfast North, where this time the UU wouldn’t field a candidate and instead pledge support for the sitting DUP MP Nigel Dodds. Belfast North is Sinn Fein’s number one target in Northern Ireland, and Nesbitt fears a divided unionist vote might lead to them winning the seat. The DUP has not formally responded to Nesbitt’s request, but it will be concerned naturally to hold on to all of the eight seats it won in 2010:

David Cameron will also be concerned to see the DUP hang on to all of these seats, for the DUP is the most likely group to which he will turn for help in propping up either a Tory or Tory-Lib Dem minority government.

Belfast North represents the DUP’s most vulnerable seat, for though Antrim South is more marginal, it is a solidly unionist constituency where the only other notional challengers are the Ulster Unionists.

Just as the DUP is the Conservatives’ natural ally in the Commons, so the SDLP fulfils the same role for Labour. It will be defending only three seats in the 2015 election, however:

All of these should be safe, but Alasdair McDonnell in Belfast South would be at risk if the unionists were to extend their pact to this seat and unite around the DUP, who came second in 2010.

Anticipating just such an outcome, yet another pact is now being talked about. This one is between Sinn Fein and the SDLP. Just last week, Martin McGuinness of Sinn Fein raised the possibility of a deal to cover the seats of Fermanagh & South Tyrone, Upper Bann and Belfast North. He suggested Sinn Fein and SDLP ought to avoid splitting the nationalist vote in these seats, thereby helping to offset the impact of any unionist pact elsewhere.

McDonnell has since rejected this idea, stating the SDLP intends to contest all 18 seats in Northern Ireland. But for such pacts to be even considered between such historically implausible bedfellows reflects the heightened sense of importance among all parties in Northern Ireland of the impending election.

And that’s not the end of the story. There are two more MPs in Northern Ireland, neither of whom belong to any of the three main parties.

One is Sylvia Hermon in Down North, who sits as an independent and who won a massive majority of 14,364 in 2010. The other is Naomi Long of the Alliance party, who won a majority of 1,533 in Belfast East.

If both are reelected in 2015, how might they cast their votes in the event of a Tory or Labour-led minority administration? Such considerations may seem trivial now, but would become a whole lot more relevant come the morning after polling day and we’re waiting to find out who Northern Ireland has decided to send to a parliament where legislation can be approved or defeated on the say of a handful of MPs.