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.

First-past-the-post is used in both general elections and local elections in England, such as in the contest in Barnsley

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.

The BBC's projected national vote share put Reform in the lead on 26%

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.