Following the results of the general election, we have been analysing different aspects of the results. This Insight looks at how the number of votes cast for each party relates to the number of seats they won.

How efficiently do parties turn votes into seats?

The first-past-the-post electoral system is well known for its tendency to produce big differences between a party’s national vote share and its share of seats. As a general election effectively consists of 650 local contests, the overall outcome depends not just on the total number of votes cast for each party, but also crucially on where these votes are cast.

In 2019, the two biggest gainers of seats were the Conservatives and the Scottish National Party (SNP). Both parties also fared well in terms of turning votes into seats. The Conservatives’ share of the UK national vote was 43.6%, but their share of seats was 56.2% (12.6 percentage points higher). The SNP won 3.9% of the UK vote but 7.4% of the seats. Looking at Scotland alone, it won 45% of the vote but 81% of Scottish seats.

Labour’s vote share in 2019 (32.1%) was closely aligned with its seat share (31.1%) although not quite as closely aligned as in 2017 (40.0% and 40.3% respectively).

As in previous elections, the seat share obtained by the Liberal Democrats (1.7%) and the Greens (0.2%) was much lower than their UK-wide vote share (11.5% and 2.7% respectively). The Brexit Party got 2% of the national vote but no seats.

How many votes cast per seat won?

The disproportionality between votes and seats can also be calculated in terms of votes-per-seat-won. In 2019 the Conservatives got one seat for every 38,264 votes, while Labour got one seat for every 50,837 votes. It took many more votes to elect a Lib Dem (336,038) and Green MP (866,435), but far fewer to elect an SNP MP (25,883).

Table showing totals of votes, seats and candidtaes for teh 2015, 2017 and 2019 general elections.

The votes that made the difference in 2019

Another way of examining the relationship between votes and seats is to look at the proportion of votes cast for a party, that were decisive in winning seats for that party. In some seats, a party may amass large majorities well in excess of the number of votes needed in order to be ‘first past the post.’ In seats where the party’s candidate is defeated, however, the votes for that candidate can be considered in retrospect to have been cast in vain.

In total, 32.0 million votes were cast in the 2019 General Election. Of these, 17.5 million votes (54.7%) were cast for winning candidates and 14.5 million votes (45.3%) were cast for losing candidates.

Within the combined tally of votes cast for winning candidates, 9.4 million votes (29.2% of all votes cast) were decisive in securing first place for the winner, while the remaining 8.1 million (25.4% of all votes) provided the winners’ margins of victory over the runners-up.

Which votes mattered?

The chart below breaks down the votes cast nationwide for each of the eight parties that won at least one seat in the 2019 General Election, based on whether the votes were:

  • decisive’ (directly contributing to a candidate coming first in a constituency – equal to the runner-up’s vote tally plus one),
  • excess’ (votes for winning candidates over and above the amount needed to come first) and
  • redundant’ (votes cast for defeated candidates).

On this basis, the party with the most efficient distribution of votes was the SNP, in that 55% of their votes were decisive in securing victory for SNP candidates, whereas only 15% of their votes were ‘redundant’ votes cast for defeated candidates. The Conservatives had the highest proportion of ‘excess’ votes (36% of the Conservative vote tally).

Chart showing breakdown of 'decisive', 'excess' and 'redundant' votes in the 2019 general election. Figures available in surrounding text

As was the case in 2017, the Liberal Democrats and the Greens were the seat winners with by far the lowest ratio of seats to votes. Both parties managed to increase their respective national vote shares in 2019 compared with 2017 but this did not translate into an increased number of seats.

The Lib Dems suffered a net loss of one seat, despite increasing their vote share by 4.2 percentage points (from 7.4% to 11.5%). The Greens increased their UK vote share by 1.1 percentage points (from 1.6% to 2.7%) but did not add to their single seat of Brighton Pavilion, which on its own accounted for 4% of the Greens’ UK-wide vote tally.

Further reading

General Election 2019: The results, The House of Commons Library.