What would the party system look like if the UK had proportional representation?

Dylan Difford, guest contributor. Opinions and research are solely the author's and do not necessarily reflect the opinions of the ERS.

Posted on the 9th June 2021

Every party system is unique – shaped by a combination of the political culture and history of a country and the rules of the voting system chosen for it. Western Europe alone presents us with a rich selection of systems varied in their breadth and purpose. As with anything even tangentially related to voting systems, the questions over what the party system would look like in a proportional Britain are often asked in electoral reform debates. Critics have tended to point to the more extreme examples. But, by looking at the experiences of similar countries and the devolved governments, we can see which kinds of party system are most probable given the sorts of voting system that are most likely to be introduced.

One of the more common scurrilous suggestions by PR’s critics is that introducing any form of PR would open the floodgates on parliamentary parties – with the new House of Commons quickly resembling the Dutch House of Representatives where 14 parties currently hold at least 2% of seats. Such high levels of multi-partyism are typically seen as undesirable as it makes government formation and stability more difficult. But the Dutch party system is only able to exist because the Dutch voting system has the lowest barrier to entry in western Europe. Due to its single nationwide constituency and 0.67% threshold, it is relatively easy to win a seat.

But no parties or serious campaign groups are proposing anything near this for the UK. The most commonly advocated for voting systems in Britain are the Single Transferable Vote (STV) – the first preference of the Electoral Reform Society – or some form of Additional Member System (AMS) – the voting systems used to elect the Scottish and Welsh Parliaments and the London Assembly. Neither STV nor AMS are particularly conducive to creating highly multi-party parliaments as parties need support in the high single-figures in at least some part of the country to win seats.

Under these voting systems we would expect the emergence of a party system more reminiscent of that seen in New Zealand, Germany or Austria. Over the last 20 years, these countries – which all have nationwide thresholds of 4 or 5% – have typically seen parliaments of between four and six parties and two-party coalition governments. The New Zealand case study is of particular note given its transition from First Past the Post to PR 25 years ago. Since then, the Labour and National parties have retained their major party status, while a few smaller but sizeable liberal, green and national populist parties have won seats at most elections. Such a party system is likely a strong contender for what might happen if Britain follows New Zealand’s path.

Similar party systems under PR have also been seen closer to home. Devolved elections in Scotland and Wales have never demonstrated anything resembling high levels of multi-partyism – the peak being the 2003 Scottish Parliament election which produced six parties with more than 2% of seats. The norm, however, has been for five significant parties in Scotland and four in Wales, with governing arrangements typically including just two parties. These low levels of fragmentation have been enabled by both the Scottish and Welsh variants of AMS having effective thresholds of over 5% in each region.

A House of Commons elected under the proportional systems that are currently proposed would most likely develop a moderately multi-party system with the Conservatives and Labour remaining as the largest, Prime Ministerial parties for the foreseeable future. They would be joined by larger, fairer blocs of a few parties such as the Liberal Democrats, the Greens and maybe one or two others, alongside the small, existing contingent of nationalist and Northern Irish MPs. Governments would typically be formed between two parties and, while other micro parties may gain the odd seat or two, this would likely be as much of a novelty as it is under First Past the Post. In all, it would be a more plural, more representative, more responsive party system, but one rooted in something familiar.

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