Current polls put Boris Johnson on course for a comfortable majority despite pro-EU parties receiving a combined 53% of the vote in Britain.
A key question for the outcome of the 2019 election is therefore whether voters on each side of the referendum debate will manage to coordinate to vote tactically in each constituency.
Tactical coordination by voters is less important for the Leave side because the Brexit party has explicitly stood down against Conservative MPs and—even more importantly—has drifted downwards in the opinion polls.
This means that most Leave voters are faced with only one clearly viable Leave option in their constituency. By contrast, tactical coordination is vital for the Remain side because there is only limited coordination between parties to stand down in seats, and Labour has not joined this agreement.
It is therefore left up to voters to coordinate within the Remain camp.
There are two main requirements needed to enable tactical voting: the voters must be willing to consider parties other than their first choice, and they must have the information required to coordinate around the best placed party in each constituency.
To examine the willingness of voters to consider other parties British Election Study respondents were asked how likely it is that they would ever vote for each party on a 0 to 10 scale. I rate a respondent as seriously considering another party if they give it a score of 6 or higher.
The following plot shows the scope for tactical voting by looking at the percentage of respondents currently intending to vote for each party (interviewed immediately before the election campaign) who would also consider voting for each other party.
The x-axis shows the pre-election vote intention of a respondent and the y-axis shows the percentage of those respondents who give a 6 out of 10 or higher to each other party.
The results show that there is substantial—but far from universal—willingness to consider other parties.
If we take voters currently intending to vote for the Conservatives, 40% of them give a high score to the Brexit Party. Brexit Party intenders return the favour, with nearly 60% of them willing to consider voting for the Conservatives.
The willingness to consider other options also holds on the Remain side. Around 40% of the people who currently support Labour, the Liberal Democrats and Greens are willing to support each other party on the Remain side.
So the willingness to consider other parties is present, but how do voters actually decide which parties have a chance of winning in their constituency?
To answer this, we gave British Election Study respondents (during the first two weeks of the campaign) a series of different options for why they might think that different parties had a chance of winning in their constituency.
The following plot shows that the most important sources of information are previous election results (particularly the 2017 election) and talking to people locally. Despite the prominence of tactical voting websites in media discussions, only 6% of respondents mention tactical voting websites as a reason for their expectations.
We also gave respondents the opportunity to give additional reasons in an open-ended format. The vast majority of these responses referred to the longstanding support for one particular party in their seat.
As one respondent pithily put it: “A monkey with a blue rosette would win here”. These responses further reinforce the importance of prior support for a party as the key indicator of its likelihood of winning.
Given that voters are citing the 2017 result as a reason for their beliefs about viability, this raises the question of how aware voters are of the result in their constituency.
The key question for tactical voting is who the top two parties are in a given constituency.
Generally, to topple an incumbent with tactical voting, voters have to coalesce around the most viable challenger. Similarly, to protect an incumbent, the voters have to know that that party is in the top two and coordinate around shoring up that incumbent party’s support.
To examine this we asked British Election Study respondents to name the winner and runner up in their constituency in 2017 during the first two weeks of the 2019 campaign.
Voters were generally good at naming the winner in their constituency, with 68% of them being able to name their MP. However, they were nowhere near as successful at naming the party that came second, with only 28% getting the correct answer.
This makes it very difficult for challengers to coordinate around the best party to take on the incumbent because most voters don’t know who the best challenger is.
While this performance is relatively poor overall, the election ultimately comes down to performance in marginal seats.
The following plot shows the percentage of respondents correctly naming the best-placed challenger according to the margin of victory in 2017. In the most marginal constituencies nearly half of respondents could correctly identify the runner up.
However, even 50% is a fairly low figure for correct knowledge of the tactical situation.
Around 40% of British Election Study respondents indicated a willingness to consider other parties on their side of the referendum debate. However, knowledge of the tactical situation is fairly low, even in marginal constituencies.
The scope for challengers to coordinate around a tactical option in each seat will therefore be pretty limited unless voters become substantially more informed about the local situation during the remainder of the election campaign.