In the 2015 GE, the voter turnout was 66.1%, not especially high, although the highest for a number of years:

This turnout meant that roughly 30m people voted, out of a possible ~46m. Turnout across the country varied greatly even among constituencies that were beside each other – in Dunbartonshire East, the turnout was 82%, compared to its neighbour Glasgow North East at 57%.

In total, just over 11m people voted Conservative, and 9m for Labour, compared to the 16m who did not vote. This article examines the hypothetical world where every non-voter was replaced by a vote for the “Did Not Vote”(DNV) party (and we’ll give them the colour turquoise).

Firstly, it is important to remember that if we used a ranked voting system, and all voters ranked every candidate (i.e. did not rank three and leave three blank), then any seat with a turnout over 50% would have to win against a DNV candidate. However, since we use First Past The Post, in any seat where the turnout was below 66.6% and the winner got below 50%, the DNV candidate must have won.

An example of where FPTP gave an unusual result would be in Belfast South (turnout 60%). Here are the results:

From this you can see that the winning party, the SDLP, only had 24.5% percent of the vote. However, this does not factor in the 60% turnout. In reality, only ~14% of eligible voters voted for the winning party, compared to 40% for our hypothetical DNV party.

While it might be easy to say that this was the result of NI’s multi-party system, and mainland Britain would never have as little as 14% deciding, the truth is not wildly different. If we examine Tristram Hunt’s seat, Stoke-on-Trent Central, we see similar numbers: although Hunt had a comfortable lead over his rivals (39.3% for Hunt, vs UKIP on 22.7% and the Conservatives on 22.5%), his constituency had the incredibly low turnout of 49.9%. When non-voters are included, this means Hunt only received 19.6% of possible votes, compared to 50.1% of voters ‘choosing’ DNV. This example both shows the incredibly low percentage of the vote that some MPs need to win their seat, and also the importance of realising that our thought experiment is very much just that, and not like the real world where Hunt enjoyed a comfortable majority. Conversely, in seats with very high turnouts, it is possible for the winning candidate to have won a lower percentage of cast votes than Hunt, but to have ‘defeated’ the DNV candidate.

So now lets look at the UK results as a whole.

To start, here are the real results of the 2015 GE, and the map of their placement.





But when we factor in our DNV party, the results change radically:

From the above, you can see that the DNV vote party is the new run-away winner. Now, the DNV have more seats than the Conservatives have in real life, and the Conservatives have fewer than Labour really have. Since the SNP only lost 7 seats, they are now ahead of Labour. Plaid Cymru lost all its seats, and every Northern Irish seat was lost, bar one for the Ulster Unionists. The Liberal Democrats lost six more seats, leaving only Nick Clegg and Tim Farron. Not included in the results is the speaker, who kept his seat.

Here are the same results on a map:

It is interesting to note that of Labour’s 43 seats, only 6 were outside the Leeds/ Wirral/ Manchester and London areas. The Conservatives tended to lose most of the cities they once had, and many of the rural constituencies along the English coastline. The SNP largely avoided losing its seats due to the high turnout, almost certainly due to the sustained political interest following the independence referendum.

Although it would impossible to create a real party like our DNV party, the above map does show possible changes to come in the next few parliaments. As the evidence shows that non-voters are more likely to come from lower-income backgrounds, it will be the challenge of both Labour and UKIP to try and convince some of the 16m non-voters if they wish to improve in 2020.