Tactical voting could have a huge impact, and I'm going to show you how.
I won't discuss the arguments for and against tactical voting, or advise you how to support specific parties—there are plenty of articles and websites about that already. My goal is to show that tactical voting is a big deal, a lot bigger than you might expect. If you want to jump right to the good stuff, check out the interactive case studies below.
This page was created by Iain Merrick. Full source code is available on GitHub. Questions, comments and contributions welcome!
Last updated: 7 June 2017
It just means: don't split the vote.
Many of the 650 seats in UK elections have results like this:
| Party | % | Vote share | |
|---|---|---|---|
| Party A | 40% | ||
| Party B | 30% | ||
| Party C | 25% | ||
| Others | 5% |
Party A wins the seat outright despite having only 40% of the popular vote.
If parties B and C are closely aligned, this is a bad result for both of them: even though they have 55% of the vote between them, they both lose. To win the seat, those voters need to vote for a single party.
This is important: tactical voting is not clever or complicated.
All the local supporters of B and C must agree which of the two parties they'll get behind. There can't be any secret strategies or special plans. If they argue over which is best placed to defeat their common enemy, they'll split the vote and they'll probably both lose. The decision must be based on hard facts.
Here's a good straightforward approach:
This isn't very fair, but it's effective.
Finally: tactical voting can have a huge impact.
Most people know the UK's "first past the post" (FPTP) system isn't ideal, but I think many don't realise just how strange the results can be, and how damaging it is to split the vote. Dozens or even hundreds of seats could be in play, as the case studies below will show.
Tactical voting usually means switching your vote from a small party to a big one. But both parties can gain seats even if one party loses votes overall. FPTP rewards concentrated local support, and punishes widespread low-level support.
In 2010, there was a 3-way vote split between the Conservatives, Labour and the Liberal Democrats, resulting in a hung parliament. After almost a week of negotiations, the Conservatives and Liberal Democrats formed a coalition government.
| Party | % | Vote share | Tactical voting |
|---|
Due to FPTP, the Conservatives and Labour got the lion's share of the seats. The Greens won a single seat (Brighton Pavilion) due to concentrated local support, but the Liberal Democrats and UKIP were under-represented.
To explore the effect tactical voting could have had, select two or more parties in the table above. Supporters of those parties will vote tactically.
This simulator just takes the raw election data and applies the simple approach suggested in the previous section:
Note that this is a very optimistic view, as it's unlikely that every single voter will agree to vote tactically for a single party. My goal here is to show the potential impact of tactical voting — and the very real impact of failing to vote tactically.
The "seats needed for majority" line takes into account the Speaker, who traditionally doesn't vote in the House of Commons, and Sinn Féin, who abstain from taking their seats.
In 2015, the Liberal Democrat vote collapsed; the SNP, Greens and especially UKIP saw big increases. The Conservatives won a surprise majority, while the SNP swept Scotland.
| Party | % | Vote share | Tactical voting |
|---|
Due to FPTP, the Conservatives gained 24 seats with only a 0.8% vote increase (smaller than that of UKIP, the SNP or Greens). Labour lost 26 seats despite a 1.5% vote increase. Apart from the SNP, other parties were under-represented, particularly UKIP (12.6% of the vote but only a single seat).
Here's the latest polling average (Tuesday, June 6) from Britain Elects:
| Party | % | Voting intention |
|---|
We'll use a very simple uniform national swing model to combine this with the 2015 results. This is not a prediction, it's for illustrative purposes only. For a real forecast, try Electoral Calculus.
I've added a second column of checkboxes here, so you can explore what happens if there are rival tactical voting groups.
| Party | % | Vote share | Tactical voting |
|---|
Note that the Conservatives have a rather large built-in advantage. I hadn't fully appreciated that until I built this simulator! But it's in line with the 2015 election results, where Labour lost seats despite gaining votes. Something about the distribution of Conservative voters is very favourable to FPTP; or it could be that Labour is too tightly packed into small areas to make effective use of their widespread support.
Please let me know if you're interested in a deeper investigation of this topic.
I hope I've shown you that tactical voting could have a big effect. If you agree, here are some things to do next: