This is part of a three-part series on the UK’s usage of Alternative Vote. For Part 1, covering the 2015 election conducted under the system, click here. For Part 2, covering the 2011 election conducted under the system, click here.

On May 5th, 2011, the UK held a referendum on adopting the Alternative Vote system, or otherwise known as Instant-runoff voting (IRV). Supported by the Liberal Democratic party as part of a coalition agreement with the Conservatives, the referendum ended in a decisive loss for those advocating for a change.

In the third part of the series, we will analyze all historical data to determine the effect of an Alternative Vote system on UK history.

Election Year Lib Dems Labor Conservatives Minor Parties
2015 +4 seats +8 seats +11 seats -23 seats
2010 -6 seats +32 seats -16 seats -10 seats
2005 +6 seats +21 seats -27 seats Not Covered
2001 +16 seats +10 seats -26 seats Not Covered
1997 +69 seats +26 seats -95 seats Not Covered
1992 +11 seats -3 seats -8 seats Not Covered
1987 +22 seats -27 seats +5 seats Not Covered
1983 +25 seats -19 seats -6 seats Not Covered
Average +18.4 seats +6 seats -20.2 seats Not Covered
Median +13.5 seats +9 seats -12 seats Not Covered

Data before 2005 is obtained from BBC’s article: Would the alternative vote have changed history?

Thus, it appears that Labor and the Liberal Democrats seem to gain the most historically, with the Conservatives seeming to lose the most historically. However the change in seats is not that high, especially in comparison to Proportional Representation, and considering how most parliaments have had in excess of 600 seats in recent years.

An interesting trend is how both center-left parties seem to benefit more from this arrangement, which is similar to what we project would happen in Canada. This is likely because both center-left parties would tend to redistribute towards each other, benefiting each other more.

We can compare how major parties support and oppose the electoral reform:

Liberal Democrats – Support

Although the Liberal Democrats seemed to prefer this arrangement due to the fact that it would redistribute votes to the center, it seems that this would not be the case in both 2010 and 2015. Indeed, a PR system would cause a much greater increase in Liberal Democrat seats – under a German-style PR/MMP system, they would be expected to net in 58 seats in the 2015, in comparison to the measly 12 in AV and 8 in the status quo.

Conservatives – Oppose

The Conservative’s opposition to this system makes sense – they would lose out in most elections if this system, or some other form of electoral reform, is implemented. Indeed, in most parliamentary systems analysed, Conservative parties tend to lose out from any electoral reform away from FPTP.

Labor – Neutral

The Labor party’s opposition to this system makes sense – although they would gain slightly in most elections if this system is implemented, the marginal amount of seats could easily be wiped out by the gains of a Liberal Democratic party growing stronger and stealing the center ground.

UKIP / Greens – Support

The fact that UKIP and the Greens supported this proposal was somewhat rational. Neither parties had much to lose from supporting the system – the total number of seats per party never broke above one in FPTP. However, in our model, neither party would pick up seats in the AV system under 2015 or 2010 election assumptions. Then again, the models created fail to account for a possible loosening of the two-party system after an AV referendum.

DUP/UUP- Support

Both the Democratic Unionist Party and the Ulster Unionist Party (both center-right, unionist, anti-republican parties) oppose a reform to AV. Although our model shows no net loss of gain for these parties, their opposition primarily seems to stem from a desire not to change the status quo – Unionist parties are largely dominant in Northern Ireland in the existing system and likely see no reason to change.

Seperatist Parties- Support

The most surprising fact was perhaps the fact that the most major separatist parties (SNP, Plaid Cymru, Social Democratic and Labour Party and Sinn Féin) supported the reform, despite our model showing no clear benefit to either of these parties in the 2010 and 2015 elections, and in the case of the SNP, a 20-seat loss. The most likely reason for this is that at the time of the referendum, separatist parties were weak in parliament, and were banking on AV to set a momentum to change to systems that these parties preferred, such as STV. In addition, at the time of the referendum, the main separatist parties appeared to be heavily disadvantaged in the FPTP system. In 2015, with the SNP controlling most of Scotland’s seats via FPTP, it would be interesting to see the appetite to change.