What would the last UK election have been like be under the alternative vote (AV)? I was discussing this question with Henry Schlechta, and I thank him for bringing it up.
The 2011 attempt at electoral reform failed, but let’s imagine it had somehow succeeded, say, for example, if the referendum had turned the other way, or if the Liberal Democrats had succeeded in getting it passed without a referendum.
In the referendum, one of the challenges the Liberal Democrats faced was that they were seen as by far the main beneficiaries of the proposed change. Conservatives and Labour alike would have been expected to rank the Lib-Dems second, and in all projections of previous elections under AV, the Lib-Dems were estimated to gain about two-dozen seats on average, even becoming the official opposition had AV been in place in 1997.
However, according to the Electoral Reform Society’s report on the 2015 general election (which presents several projections of the results of the election had it been held under a different electoral system), the 2015 general election would have hardly been any different under AV:
||Seats under AV
||Difference from actual seats
In fact, not only would the Liberal Democrats have received just one seat more than under First Past the Post, the main beneficiaries apparently would have been the Conservatives, who were hell-bent on preventing the system’s adoption in the 2011 referendum campaign.
It would seem that the Lib-Dems lost so much support in 2015 that there would have been far fewer seats where they were among the top two parties in first-preference terms, thus being able to survive exclusion until the final round where they could benefit from Labour or Conservative lower preferences. Perhaps they also lost so much credibility that they would get fewer lower-preferences than in previous elections (I couldn’t find the full poll results on which the projection is based – I would be very grateful if someone else were able to share them with us).
Of course, this is just a projection, with some serious limitations. Firstly, it appears votes under FPTP were simply translated into first preferences. In reality, many voters who voted strategically under FPTP would use the opportunity given to them by AV to rank their real first preference first. Secondly, AV might incentivise parties to pursue different campaign strategies, and maybe even have an impact on manifestoes and candidates, as the need to get a majority of the vote would change what it takes to be elected in many constituencies.
In any case, there would probably have been more 1st-preference votes for smaller parties, including UKIP and the Lib-Dems. But the Lib-Dems might also have benefitted from second preferences from parties such as the Greens, who would usually get eliminated from the count first. Might this have evened out the effect of the Lib-Dem collapse in some constituencies and allowing the Lib-Dems to beat the Conservatives to the final ‘round’ on preferences, by getting second preferences from parties smaller than UKIP?
What would have become of the Conservatives’ campaign warning against a minority Labour government dependent on SNP support? Could it easily have become a campaign for voters’ second preferences?
In Scotland, would Unionist parties have recommended preferences to each other to block the SNP?
These are just a few of the questions that should be considered when constructing this alternate history, and I’d love to hear our readers’ thoughts on these as well as other potential changes to the campaign and results if the UK had adopted AV in 2011 (or any other country – there’s at least one that has been discussed here where the question is becoming increasingly relevant).
 Based on second- and third-preference polls. The methodology is stated in appendix of the report (page 33).