The issue of tactical voting is looming large in discussions about how the 2019 general election will play out.
Tactical voting happens when a voter abandons the party or candidate they prefer, and votes for one with a better chance of winning locally – often, but not always, in order to defeat a disliked candidate.
Relatively small changes in the number of votes a candidate receives have the potential to make a big difference.
At the 2017 election174 MPs were elected with less than half the vote,and in 2015it was 334 out of 650. In those constituencies, supporters of the parties that came third place or lower, could have defeated the MP by backing the second-placed party.
How many people vote tactically?
Surveys after recent elections saw about one in 10 voters – around 3 million people – saying they voted tactically.
Percentage of general election voters in Great Britain reporting that they voted tactically
The number of people voting tactically has not changed very much since the 1990 s, despite the fact that peopleswitch votes between elections more frequently.
It seems that tactical voting is not driven by political sophistication or general willingness to consider switching, so much as how much support there is for lower- placed candidates in constituencies, and how much supporters of those lower-placed candidates like their second-choice party and dislike one of the top contenders.
Tactical voting is not particularly more likely to happen in closely fought constituencies, where a relatively small number of voters can make more of a difference. People often vote tactically in relatively safe seats too.
Since it is not always clear what order the parties are going to come in, some voters make mistakes and vote tactically the wrong way – that is, for a party that ends up doing worse than the voter’s preferred party.
Typically though, people are more likely to vote tactically the clearer it is that their preferred party is out of contention.
When has tactical voting worked in the past?
In the 1990 s, after the Conservatives had been in power for over a decade, Labor and Liberal Democrat supporters were often willing to vote tactically for each other depending on who was best placed to defeat the Conservatives locally.
This reacheda high point in 1997when tactical voting was estimated to have cost the Conservatives around 46 seats, with Labor taking 35 and the Liberal Democrats 11 of them.
However, if tactical voting fails to happen in large enough numbers, it doesn’t make a difference.
At the 2015 election, shortly after the Scottish independence referendum, there was an attempt to co-ordinateanti -nationalist tactical votingamong opponents of the Scottish National Party (SNP). It even involved Conservative supporters voting Labor.
It almost certainly saved Labor from a total wipe-out in Scotland, securing their one remaining seat north of the border that year. But it was not enough to stop the SNP fromwinning nearly all the seats(56 out of 59) with just less than half the overall vote in Scotland.
How could tactical voting work at this election?
Tactical voting in the 2019 general election is likely to be shaped mainly by divisions over Brexit, even more so than it was in 2017.
Among Leave supporters, tactical voting is likely to come into play in constituencies where the Brexit Party and the Conservatives are competing to take a seat from a party that is sympathetic to another referendum (the Brexit Party has alreadystood down its candidatesin seats that the Conservatives won last time).
The Conservatives’ message – “get Brexit done” – is aimed partly at encouraging Brexit Party supporters to use their vote tactically in seats where the Conservatives have a better chance of winning (that is, most, if not all, of them).
Tactical voting among Remain supporters is much more complicated because it involves more parties, withvarying Brexit policies.
The Lib Dems the SNP, Plaid Cymru and the Green Party are all pro-Remain. The Labor Party is in favor of a referendum but has not committed to supporting Remain or Leave.
Pro-Remain parties also disagree on other issues, and they do not always say nice things about each other’s party leaders. For all of these reasons, many supporters of these parties are not keen on switching tactically in favor of one of the others.
It is often difficult to identify Remain candidates best placed to win seats from Conservatives. This is because different pro-Remain parties did well in different places at the last general election.
Party support:2 December 2019
Party Average (%) Likely range
CON 42 (38 – 46)
LAB 31 (27 – 35)
LD 14 (10 – 18)
BRX 4 (0-8)
SNP 3 – *
GRN 3 (0-7)
PC 0 – *
UKIP 0 – *
TIGfC 0 – *
What’s more, there have been big changes in the opinion polls since 2017. On average in the polls, the Labor vote has dropped by 10 percentage points since the last election, while the Lib Dem vote has increased by six points.
This suggests the Lib Dems may have overtaken Labor in as many as (of the) seats where Conservatives are defending and Labor came second last time.
Tactical voting websites
At this and previous elections there have been constituency polls to guide people in some high profile places. Now there are also sophisticated statistical models of polling data attempting to show how support for the parties stands in every constituency.
These models have been used by campaign groups to set up websites encouraging people to vote tactically for particular parties in particular constituencies.
Some go so far as to organize vote swapping – matching people from different constituencies so they can both vote tactically, knowing that someone somewhere else will be voting for their preferred party.
Tactical voting websites largely agree on which pro-Remain parties are best placed to win in which constituencies, but they do not entirely agree.
There have also been changes in public opinion since those websites were set up, and there might well be further changes before election day. And, of course, all polls and forecasts may be inaccurate.
So tactical voting websites cannot be entirely relied on. Voters have to form their own judgements as to whom they want to vote for and why.
About this piece
This analysis piece wascommissioned by the BBC from an expert working for an outside organization.
Stephen Fisher is associate professor in political sociology and a fellow of Trinity College, Oxford
Edited by Ben Milne