Consider the following bizarre potential outcomes for the 2015 general election:

The SNP romp home, winning well over 20 seats. The Green Party also do the best they’ve ever done, gaining 5% of the national vote. Yet the latter party only win a single seat despite getting a higher UK share of the vote than the former.

UKIP do the best they’ve ever achieved in a general election, with 16% of the vote. They only win around half a dozen seats however. The Lib Dems meanwhile creep home with just 15% of the vote, yet hold onto over 20 seats.

Labour gets slightly fewer votes than the Conservatives. Despite this poor performance, they win more seats than their opponent. Their total vote share hovers at around 60% of the vote, the lowest combined score since 1918.

No single party gains a majority. More than that, no two party majority is possible, with the exception of a Labour-Conservative coalition.

I’m not suggesting that all of these outcomes are going to happen, merely that at this point in time they are all feasible. If they do all happen at once, it will be the perfect storm of electoral outcomes which will put our single member plurality voting system (“SMP”)* under greater strain than it has ever known.

This has in fact been a long time in coming. The reality is that “two party politics” is a historical quirk that has only enjoyed a very brief period of popularity. The modern political party as we now regard it didn’t even exist when the Third Reform Act was passed in 1884 enfranchising most men over the age of 21. 16 years later the Labour Party was born and we had decades of 3+ party politics until the Liberals pretty much gave up the ghost in the 1930s and 40s. In 1951, two party politics reached its apex with the combined Labour-Conservative vote reaching 96.8% but by 1974 that was down to 75.1% and in long term decline.

We can see this trend by looking at how the gap between Effective Number of Parties (“ENP”) by votes and seats has widened over the last 70 years (ENP is an academic concept used to estimate the number of parties active in an election according to their relative strengths). As you can see, the disparity between votes and seats has widened almost inexorably.

Indeed, it is also worth bearing in mind that the voting system itself was stitched up to reinforce this hegemony. SMP is not, in fact, the only voting system to have been used in a House of Commons election. Multi member constituencies were quite common for urban areas at first, and university seats were elected using Single Transferable Vote from 1917 until 1950. You can see how, in the first decade after single member constituencies were universally adopted in 1950, the disparity between votes and seats actually got worse. By contrast, if we had not gone down that route, it seems likely that UK elections would have done a better job at reflecting votes cast.

Josep Colomer asserts that as political systems embrace multi-party politics, they tend to drift inexorably towards proportional representation.

A crucial point, however, is that coordination failures can be relatively more frequent under majoritarian electoral systems, especially for the costs of information transmission, bargaining, and implementation of agreements among previously separate organizations, as well as the induction of strategic votes in favor of the larger candidacies. With coordination failures, people will waste significant amounts of votes, voters’ dissatisfaction with the real working of the electoral system may increase, and large numbers of losing politicians are also likely to use voters’ dissatisfaction and their own exclusion, defeat or under-representation to develop political pressures in favor of changing to more proportional electoral rules.

In other words, eventually the ability to “do politics” using a majoritarian system becomes increasingly difficult as more parties become effective agents within the system. He goes on to suggest that “above 4 ENPs, establishing or maintaining a majority rule electoral system would be highly risky for the incumbent largest party, and possibly not feasible either due to pressures for an alternative change supported by a majority of votes.”

Sadly Colomer doesn’t actually tell us how this switch will happen, but we are already seeing the current system falling apart. Of all the potential outcomes I listed at the top of this article, the biggest problem from a governance point of view is that difficulty we might encounter in forming a government. In 2010 (and despite the more fruity speculation by some), the arithmetical logic behind the Conservative-Lib Dem coalition was quite straightforward: there was simply no other way to form a two party coalition, apart from a Conservative-Labour one of course. Despite some sunny optimism about the viability of a Labour-LD-SNP-Unionist government, the fact is that such a rainbow would have been incredibly hard to maintain.

A lot of political commentators have asserted that the outcome of the 2015 general election is impossible to predict. They are only half right. It’s actually quite clear which way people are going to vote; what is unpredictable is a voting system that is so poorly suited to its purpose that the numbers that it chews out could go anywhere. That this doesn’t lead more people than it does to declare that it is time to pick another system is a sad testament of how badly let down our media and politicians are letting us down.

After the 2011 AV referendum, the No campaign declared the matter of the voting system settled for a generation. The 2014 Scottish independence referendum has already demonstrated to us how such things are rarely that simple, and it seems likely to me that the debate over whether SMP is any longer fit for purpose will kick off in a big way after this year’s election. At least, it will among the public. The question is whether civil society and the media will join that throng or allow it to peter out. It can’t be left to the Electoral Reform Society and Unlock Democracy to make the case.

And how will the political class respond? Will they embrace the tide of history in the way that they did eventually over the Reform Acts and female suffrage, or will they continue to resist it? I hope they’ll take the pragmatic, former option; if they don’t we could be looking at decades of instability. For me, it’s the only truly interesting question about this year’s general election; until we have a system which in some way reflects the settled will of the people, everything else will just be a case of rearranging the deckchairs on the Titanic.

* Personally I prefer to refer to the UK voting system as “single member plurality” and not “first past the post”. This is for several reasons. Firstly, it is a simple fact that it better describes the actual system: we have single member constituencies and you win by getting the plurality (largest share of the vote). “First past the post” on the other hand doesn’t actually describe how the system works at all – ironically, to the extent that it describes anything, it better describes the Alternative Vote system/instant run-off voting which actually has a “winning post” (50%). Secondly, it is the internationally recognised description of the system; the UK loves its quirky and confusing names for voting systems (Additional Member System instead of Multi Member Proportional for example), and it is a fairly contemptible bit of British chauvinism. Thirdly, I think that allowing the supporters of SMP to use their preferred, familiar term puts them at an advantage as all other voting systems sound alien and technical in comparison. That’s nonsense, and I don’t think we should allow them the privilege.