Written by Thomas Worth
The results of the 2024 General Election were the most disproportional in British political history. The current Labour government was elected on just 33.7% of the vote, but took 63.2% of the seats, while smaller parties like Reform UK and the Greens won less than 2% of the seats between them on a combined 21% of the vote. Numbers like these lay bare how unsuitable First Past the Post is in an era of multi-party politics.
While the disconnect between the percentage of votes and the number of seats won is a clear signifier of a broken electoral system, there are other metrics that can be used to measure the ineffectiveness of First Past the Post.
What is the Effective Number of Parties (ENP)?
This brings us to the concept of the Effective Number of Parties (ENP). This tool was developed by the political scientists Markku Laakso and Rein Taagepera in 1979 as a measure designed to analyse the political fragmentation of a chosen political system. Rather than just a count of all the parties within a system, the ENP calculates the weighted number of parties that matter within a system. This can be done either in terms of their vote share (the Effective Number of Electoral Parties or ENEP) or on seat share (the Effective Number of Parliamentary Parties or ENPP).
It is important to note that the figure does not represent the actual number of parties within a system but is instead a measure of fragmentation. Taking Canada as a recent example, the Effective Number of Electoral Parties after the 2025 Federal Election was 2.70, while the Effective Number of Parliamentary Parties sat at 2.36. This means that electorally, the party system is as fragmented as if there were 2.70 equally sized parties.
This concept allows us to compare political fragmentation across countries and is a method frequently employed by political scientists. The ENP also provides us with a useful tool to understand how electoral systems constrain political parties and limit the number of those who, while being electorally significant, gain representation in the legislature.
Fragmentation in the UK
Turning to the UK, the disproportionality of our electoral system is laid bare by the difference between our ENEP and our ENPP as per Michael Gallagher’s Election Indices. After the 2024 General Election, our ENEP stood at a mighty 4.76, the highest it has ever been. Only the 1918 General Election comes close to our current figure on an ENEP of 4.42. Meanwhile, our EPP stands at 2.24, the lowest since 2001 and significantly lower than 2019 despite the combined vote share of the major parties falling in 2024.
Supporters of the status quo claim that a benefit of the current system is that everyone votes either for the government or the opposition who are primed to replace them. Yet, electorally our political system is as fragmented as if there were 4.76 equally sized parties, something that should not occur under a ‘functioning’ First Past the Post system. The difference between our ENEP and ENPP clearly shows that First Past the Post can no longer account for how voters are expressing their electoral wishes.
Fragmentation around the world
When drawing comparisons with other countries, it is clear how poorly performing First Past the Post is in the UK. A functioning electoral system should have an ENEP and ENPP that are closely matched, meaning that seats broadly match votes and that parties are gaining representation based on their electoral performance. Countries using the proportional Single Transferable Vote, such as Malta, see much more alignment between their ENEP and ENPP. Malta has one of the closest of any democratic state with an ENEP of 2.09 and ENPP of 1.97 in 2022. Meanwhile, Denmark, using D’Hondt party-list PR, had an ENEP of 7.57 and an ENPP of 7.24 in 2022.
What these cases show is that the system of First Past the Post in the UK is no longer functioning effectively as the gap between our ENEP and ENPP has been growing ever wider, meaning that as the electorate increasingly fragments, our system is failing to reflect their preferences. Meanwhile, more proportional systems are able to cope with fragmentation and see close alignment between the number of electoral and parliamentary parties.
New Zealand’s journey to proportional representation
This should be an impetus for change, and the Effective Number of Parties also provides case studies which can give electoral reformers hope. Evidence suggests that as the ENEP increases, the likelihood of electoral reform increases due to the pressures fragmentation places on a disproportional electoral system. People start voting for more parties, which leads to proportional representation, not the other way around.
The prime example of this is New Zealand, a country often lauded by proponents of electoral reform for its shift from First Past the Post to Mixed Member Proportional (MMP) known as the Additional Member System (AMS) in the UK. The ENEP of New Zealand steadily rose before the changes were implemented in 1996, with fragmentation creating pressure for reform. From a low point of an ENEP of 1.99 in 1951, by the time of the referendum on electoral reform in 1993, the ENEP stood at a high 3.52. The ENPP, meanwhile, failed to match the increase with First Past the Post, continually providing disproportional results. 1993 was a particularly bad year, with the ENPP standing at only 2.16.
After switching to MMP, the ENEP and ENPP are now closely aligned, standing at 4.10 and 3.81, respectively, in 2023. What this proves is that a shift towards a more proportional system will allow the increasing political fragmentation of our party system, which is higher than in New Zealand under MMP, to be better reflected in Parliament.
Therefore, in order to achieve a closer alignment between the effective number of electoral and parliamentary parties, it is crucial that the UK learns from the lessons of New Zealand and begins to reform the electoral system in order to remedy the growing disconnect between how people are voting and how they are represented in parliament.
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