How the winner-takes-all voting system has turned on Labour and the Tories

Under the first-past-the-post electoral system, the candidate or candidates with the most votes in each seat are elected. It is used in the UK at general elections and in local elections such as the ones just held in England.

An alternative is a system of proportional representation under which some attempt is made to distribute seats to reflect the popularity of parties. Both the Scottish Parliament and the Senedd in Wales use systems of proportional representation.

First-past-the-post has long been regarded as a friend of the Conservative and Labour parties.

It makes it difficult for small parties whose vote is evenly spread geographically to win seats. This helps to keep potential challengers to the Conservatives and Labour out of the House of Commons. Indeed, because that is the case, voters may be reluctant to vote for them in the first place.

Historically, the system has also given whoever is the victor in the electoral battle between Conservative and Labour a boost in seats. The two parties thus both get the chance of securing a period of untrammeled majority government rather than having to negotiate the rocky shores of minority or coalition government.

However, Thursday's election results raise questions about whether first-past-the-post will continue to benefit the Conservatives and Labour in future. Rather, they have shown that the system is colour blind in how it operates

The results confirmed that Britain has now entered an unprecedented era of multi-party politics. According to the BBC's projected national share, if the whole country had had the chance to vote in a local election on Thursday Reform would have come first with 26% of the vote and the Greens (narrowly) second on 18%. The Conservatives and Labour would have been left with just 17% each. Their joint tally of 34% represents a record low. Even the Liberal Democrats – who regularly perform relatively well in local elections – were not far behind on 16%.

This not long after fewer than three in five people voted Conservative or Labour in the 2024 general election. That was the lowest proportion since and including 1922, when Labour first became the Conservatives' principal competitors.

This rise in third party voting suggests that first-past-the-post is no longer proving effective at discouraging people from backing parties other than Conservative or Labour. Once upon a time, Conservative and Labour politicians would cry, 'A Liberal vote is a wasted vote'. That kind of argument has seemingly lost its force.

Moreover, those who voted for Reform and the Greens have now seen that a vote for their parties can in fact result in them winning seats. With just a handful of results yet to be declared, the joint tally of council seats won by Reform and the Greens stands at 2,063, almost 200 more than the total of 1,864 won jointly by the Conservatives and Labour. Meanwhile, Britain's traditional third party, the Liberal Democrats, have won 842 local council seats too.

This is a very different picture from the 2024 general election, when the Conservatives and Labour won 533 seats, while Reform and the Greens jointly were left with just nine, despite scoring over 20% of the vote between them.

Labour and Tory losses amplified

Indeed, rather than helping to insulate the Conservatives and Labour from the challenge posed by the new challengers, the system served on Thursday to exaggerate the loss of support they were suffering in the ballot box.

For both Labour and the Conservatives, their share of the vote fell most heavily in wards they were trying to defend. In a sample of more than 1,000 wards where the BBC has collected the detailed voting statistics, support for Labour fell on average compared with 2022 (the year when most of the seats being contested on Thursday were last fought over) by 25 points where the party was trying to defend the seat. The drop was just 12 points in the seats they were not defending. In the case of the Conservatives the equivalent figures are 14 points and 10 points respectively.

Such a pattern inevitably meant that the loss of seats that the two parties suffered – more than 1,400 in the case of Labour and more than 500 in the case of the Conservatives - was higher than it would otherwise have been.

In this new era of multi-party politics, the first-past-the-post system also delivered Reform a majority in a number of councils despite winning less than half the vote in them. In the BBC's sample of detailed voting results, there are eight councils where Reform won a majority of the seats being contested this year despite winning less than half the vote. Examples include Dudley, Plymouth and Rochdale. Indeed, Reform won more than half the seats on less than half the vote on more occasions than either the Conservatives or Labour.

Moreover, the boost that Reform sometimes enjoyed was in some instances considerable. In those councils where the party won more than half the seats, Reform won just 36% of the vote on average. Yet this proved sufficient for them to secure as much as 67% of the seats.

A similar discrepancy is evident in the equivalent figures for the Conservatives and Labour. Most notably, Labour won just 29% of the vote in both Ealing and Merton in London, yet this was still enough to put the party at the head of a very crowded field in both. As a result, the party won 66% and 56% of the council seats respectively.

Under first-past-the-post, what matters is not the absolute share of the vote that a party enjoys but rather how well it has performed compared with other parties. Under fragmented politics that means a relatively low – but still winning - share of the vote can enjoy a highly disproportional reward. As a result, it can open up the prospect of governments – including even majority governments – being elected on relatively low shares of the vote.

Winning by losing less

Indeed, first-past-the-post even means that a party that is losing support at the ballot box can still make significant gains in terms of seats if its principal opponents are losing votes even more heavily. This is what happened in the one council where the Conservatives gained control, Westminster. Support for the party fell by five points in the borough. However, support for Labour, who were defending their control of the council, fell by even more – 17 points. The Greens won 17% of the vote but no seats and the upshot was the Conservatives were able to gain control.

In the case of the Liberal Democrats, this phenomenon was evident more broadly. The party's support was down on average by four points compared with four years ago. This was even true of the wards the party won. Yet this did not stop it making a net gain of nearly 100 seats, thanks to the fact that both Conservative and Labour support was falling even more heavily.

As a party that was simply just one of a crowded pack rather than, like Reform in the lead, the system inevitably was kind to the Greens in fewer instances. That said, in Manchester, the party was able to win 56% of the seats at stake off the back of just 37% of the vote. Equally, its success in denying Labour control of both Cambridge and Exeter was aided by favourable treatment from the electoral system.

No definite majority

Yet despite first-past-the-post's tendency to be kind to winners, when the political field becomes as crowded as it is now, it is far from guaranteed that it will produce an overall majority for any one party. One in three of the 63 councils where all the seats were up for grabs on Thursday are now in no overall control. Before Thursday only half a dozen of them were in that position.

Even first-past-the-post cannot be relied upon to avoid the prospect of minority or coalition government if electoral support is shared across a plethora of parties.

If it continues, Britain's fragmented politics creates the prospect of significant changes in the way elections are fought, parliament is run, and governments rule. The results of Thursday's local elections suggest that it may see the country's first-past-the-post electoral system operate in an unfamiliar manner too.

John Curtice is Professor of Politics, Strathclyde University, and Senior Fellow, National Centre for Social Research and 'The UK in a Changing Europe'.

Analysis by Patrick English, Steve Fisher, Robert Ford, Lotte Hargrave, Jonathon Mellon and Stuart Perrett

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