On Monday, attendees of the UK Labour Party conference voted in favour of including a pledge to introduce proportional representation into its manifesto for the next general election. Of course, Proportional Representation can mean many things, so in this series of articles I’ll be looking at the effect of different variations of PR on the UK Parliament.
Today, I’ll be looking at the effects of various thresholds for getting into Parliament. Over the course of the next few days, I’ll also look at different proportional formulae, the use of mixed-member proportional representation, and the sizes of individual regions.
For these examples, I’ll be using the results of the 2019 election as the inputs to these calculations, with an acknowledgement that many voters would vote differently under PR than under the current First Past The Post system. I’ll be allocating seats to the nations and regions of the UK according to their mid-2020 population estimates, and for today I’ll be using the d’Hondt for allocating seats between parties and between regions.
Purest Proportional
The purest form of proportional representation means that any party that gets 1/650 (0.15%) of the vote would get a seat in Parliament.
With no minimum thresholds and no regional breakdowns, only two parties would enter the House of Commons who didn’t get seats under First Past The Post. The Brexit Party would have won 13 seats in the Commons on a 2% vote share, while the Ulster Unionist Party in Northern Ireland would have won one seat on a 0.3% vote share. The largest party to have missed out would have been the Yorkshire Party, finishing with just under 0.1%.
Nationwide Minimum Vote Share
It’s very common with proportional representation have a minimum vote share required to enter Parliament. This threshold is most commonly set at 5%.
At the last election, only three parties reached 5% of the vote nationwide, with none of the regional parties (including none of the parties which run in Northern Ireland) winning any seats. So this clearly won’t do.
A common variant of this, in a mixed-member proportional system, is to open up seats in Parliament to any party that either wins 5% of the nationwide vote, or wins in at least one constituency. If we assume that every party that won at least one seat in 2019 would win one constituency under MMP, that would give something close to the pure proportional result, but without the Brexit Party or Ulster Unionists entering the House.
Breaking Down by Regions
Another way to strike the balance between letting parties with concentrated regional support into Parliament while keeping parties with thin support out is to allocate seats on a region-by-region basis. This would mean it wouldn’t be enough to get 0.2% of the vote nationwide, but they would need between 1–5% (depending on the region) to get any seats.
This produces a very slight difference with the pure PR scenario at the top. The first difference is the distribution of seats between larger and smaller parties in Great Britain; the Brexit Party wins seats in only half of the regions, and the LibDems and Greens end up with fewer seats overall, while the Conservatives and Labour finish a few seats ahead of where they would otherwise have been. The other notable thing is that, with pure PR, the parties of Northern Ireland would only finish with 13 seats between them, when their population means they should have 18 seats. This is because a lower share of the population of Northern Ireland tends to vote relative to the UK as a whole.
We can also look at putting a 5% threshold on each region, to further reduce parties with thin support entering Parliament.
Adding a 5% threshold to each region would mean the Green Party wouldn’t enter the House of Commons at all, while the Brexit Party would only miss out on three seats in two regions. Most of those seats would go evenly between the Conservatives and Labour.
Subtle changes to the rules determining whether a party is eligible to enter the House of Commons can make a material impact on a party’s representation, or lack thereof, in the House of Commons. Finding the balance between strong regional voices getting into Parliament and keeping weaker voices out is a tricky balance to strike; getting it wrong could mean a sizeable share of the population doesn’t get their voice heard in the corridors of power, while getting it wrong the other way could mean harmful voices make their way into those same corridors of power (2010 would have been such an example). It’s just one part of deciding upon a system of proportional representation that requires extra thought.
