Today's UK by-elections are set to demonstrate the effect of spoiler candidates on a First Past The Post ballot.
In the UK it is pretty clear that First Past The Post (FPTP) benefits the right-wing Conservative party at the expense of the centrist and left-wing Lib Dem, Green and Labour parties.
Are there any countries where this effect is reversed and a singular left wing party gains over a splintered right wing group of parties?
First past the post systems provide representation in elected offices that is disproportionately high relative to the percentage of people who support a political party or group if:
The group is a majority or more of the total population, and/or
The group's members of geographically clustered rather than diffusely spread out geograhically.
For example, in a country with 100 seats in the legislature, a party with 3% of voters whose voters are almost entirely concentrated in five electoral districts where it makes up 60% of the voters in each district, could win 5% of the elected offices.
But, a party with support from 30% of voters who are evenly spread across the entire country, might fail to win even a single seat in the legislature.
More generally, the more geographically sorted people are by politics, the less distorting a first-past-the-post system will be. If people are geographically blended politically, the smaller parties get hammered and the large parties receive disproportionate gains.
The left wing or right wing leaning of a political party isn't facially relevant to these criteria.
It is somewhat difficult to find all of that many real world examples because most countries that lean left have adopted some manner of proportional representation in their electoral systems driven by "good government" ideals, and there aren't all that many countries in the world, period, that still have pure first past the post election systems.
Even in the United States, not all U.S. states have that system. See, e.g. Alaska, Hawaii, and Maine, which use some variation of ranked choice voting in some state-wide elections.
Countries that primarily use a first-past-the-post voting system for national legislative elections (Source)
The first-past-the-post system is now used predominantly in national legislative elections in Canada, the U.S., the U.K., Liberia, and in some former British colonies in the Caribbean, Africa, South Asia and Southeast Asia. It is also used in a couple of small outlier countries that were never subject to British rule (e.g. Belarus and Azerbaijan).
Moreover, many of the nominally first-past-the-post system countries in former British colonies in Africa and Asia have been dominant party systems or one party political systems for much of their democratic history. Belarus and Azerbaijan are authoritarian dominant party systems with unfair elections.
Many U.S. states for much of its history have also had dominant party systems.
Some of the dominant parties in these systems are nominally left wing rather than right wing, but since the elections are often flawed in other respects, and one party is so dominant, it is hard to link these outcomes to the first-past-the-post system per se.
Usually geographically concentrated parties like this are ethnic nationalist parties, although this isn't necessarily the case.
For example, Canada's multiparty system has been driven by geographically concentrated party preferences with the left leaning Quebec's Nationalist party dominating that province and being overrepresented relative to its vote share, while Western Canadian provinces had one dominant conservative party, and Eastern Canadian provinces had another dominant conservative party, and the Anglophone Canadian left was united, for many years.
Another answer notes, this is also true of the Scottish Nationalist party, which is left-leaning and disproportionately represented in Scottish Parliament elections. (It also is disproportionately represented in U.K. national parliament elections.)
As another example, the left leaning parties of Turkey receive almost all of their representation from ethnic enclaves in far eastern and southeastern Turkey, and would do better in a first past the post system there than they do in Turkey's more proportional representation oriented electoral system.
For example, England's new defunct Liberal Party, while it has significant numbers of voters, has voters who are distributed in a diffuse manner across England and almost always underperformed their raw share of votes for the British Parliament in England's first past the post system.
For example, in 1983, the Liberal Party in the U.K. won 25.4% of the popular vote in parliamentary elections, but won only 2.6% of the seats in the House of Commons.
Whether the Liberal Party can properly be counted as a part of the left or the right is another question. To some extent, its difficulties stem from the fact that is isn't precisely either a left wing or a right wing party and instead is stuck in the middle.
For example, in Wyoming, after the 2020 elections, out of 60 state representatives, Democrats held 6 seats, and out of 30 state senators, Democrats held 2 seats, for a total of less than 10% of the state legislative seats in the state, despite the fact that the Democratic candidate won more than 26% of the vote in the 2020 Presidential election.
Few blue states are so lopsided, but Democrats do win a disproportionate share of legislative seats in blue states in the U.S. relative to their share of the votes cast in state and federal legislative elections, primarily due to the first-past-the-post system used in most U.S. states, and secondarily, due to the gerrymandering that this system facilitates.
For example in 2022, in California, Republicans won 12 out of 50 U.S. House seats. But, 29% of Californians voted for Republican Presidential candidate Donald Trump in 2020. So, Democrats slightly over performed in the first-past-the-post system election in 2022.
In 2015, in the Canadian province of Alberta, after the Wild-Rose party split from the conservatives, the left wing NDP won a majority of seats (for the first time ever) with only 40% of the vote, while the 2 conservative parties had the other 60%: https://en.wikipedia.org/wiki/2015_Alberta_general_election
By the next election, the 2 conservative parties patched up their differences and as the "United Conservatives", predictably crushed.
That is, of course, if you consider the Scottish National Party a "left-wing or centrist" party and not "conservative", which I think is fair despite their nationalist postion and considering their membership in the European Free Alliance.
Also, Scotland has not a pure first-past-the-post system but a mixed Additional Member system, where every voter has two independent votes. According to Wikipedia
73 MSPs represent individual geographical constituencies elected by the plurality (first-past-the-post) system, while a further 56 are returned as list members from eight additional member regions.
But it clearly still favours the party that wins the most constituencies. The effect is not as pronounced, but still observable, as seen in the result of the last three elections:
| Year | Constituency vote | Regional vote | Seats |
|---|---|---|---|
| 2011 | 45.4% | 44.0% | 53.5% (69 / 129) |
| 2016 | 46.5% | 41.7% | 48.8% (63 / 129) |
| 2021 | 47.7% | 40.3% | 49.6% (64 / 129) |
Are there any countries where this effect is reversed and a singular left wing party gains over a splintered right wing group of parties?
The Scottish example shows that it is not really needed that the favoured "side" consists of a smaller number of parties than the penalized one. Of the five parties currently represented, three would be considered left (SNP, Labour and Greens), while two would be considered centrist or right (LibDem and Conservative). The largest party is always favoured to win.
That pretty much just happened in the UK - specifically Tamworth.
It looks like there was tactical voting for Labour by Liberal Democrat and possibly Green supporters but, interestingly, if the voters for UKIP, Britain First and Reform had voted tactically for the Conservatives, the seat might have been held.
| Party | Candidate | Votes | % |
|---|---|---|---|
| Labour | Sarah Edwards | 11719 | 45.8 |
| Conservative | Andrew Cooper | 10403 | 40.7 |
| Reform UK | Ian Cooper | 1373 | 5.4 |
| Britain First | Ashlea Simon | 580 | 2.3 |
| UKIP | Robert Bilcliff | 436 | 1.7 |
| Green | Sue Howarth | 417 | 1.6 |
| Liberal Democrats | Sunny Virk | 417 | 1.6 |
| Monster Raving Loony | Howling Laud Hope | 155 | 0.6 |
| No description | Peter Longman | 86 | 0.3 |
Voting figures from Wikipedia
I do not know if this is a good example, but Belarus uses the first past the post system, and the leading political party in the last election in 2019 was the Communist Party of Belarus, with 11 seats in the legislature out of 110. The majority of the seats (89) though got the non-partisan representatives. The runner-up political party was Republican Party for Labor and Justice with only 6 seats, which is twice less than that of the Communist party.
