Record-breaking council by-election trends means candidates more likely to win with less voter support, study warns

The growing trend of record-breaking council by-election results will mean more close contests and more candidates winning with little voter support, a new report warns.

Last year saw an increasing number of closely fought contests between multiple parties, a pattern likely to continue, meaning every vote will count this May.

The profound changes in the electoral landscape means future gains will be achieved on smaller margins, according to analysis by Hannah Bunting and Michael Thrasher, from the University of Exeter’s Elections Centre.

Last year six, seven and eight candidates from different parties were on the ballot in a third of the 308 single-vacancy council by-elections. Throughout much of the past 40 years there have been such a large number of candidates in just 7 per cent of elections, and in 2024 this was the case in a fifth of elections.

The analysis shows how this can be explained by the exponential increase in the Green Party and Reform UK’s local election presence. In 2025 Reform fielded 290 candidates for 319 vacancies across England and Wales – a rate of 91 per cent and an almost four-fold increase on the previous year. Over the past two years the Green Party has contested three quarters of vacancies.

In 2025 the electoral support required to win a seat in council by-elections fell to its lowest level. The number of candidates contesting an election with a realistic chance of success increased. The gap between the votes achieved by the first and second-placed candidates narrowed to its lowest margin.

Up until 2025 the mean average vote share for a winning candidate was 52 per cent. The record high share, 55.4 per cent, was established in 1997.

In 2025 there was a new record average of 44.2 per cent vote share needed for those council election winning their seat. The consequence is that some candidates are successful with very little support.

Dr Bunting said: “Last year saw profound changes in the electoral landscape, affecting the competition for seats, the distribution of votes and a decline in vote share required for winners. This is a departure from the previous forty years of contests and has implications for who will win this May, and how they will win.

“More candidates are standing for more parties and more voters are choosing to vote for parties across the range of those standing than ever before.”

In 2025 a total of 20 contests were settled after the winner secured fewer than three in ten votes.

As well as the percentage vote for success shrinking, in 2025 another record was established for percentage majority as contests became tighter. In 1995, the average by-election majority – the difference between the winner and second place – reached a maximum of 25.7 per cent, with a long-term average before 2025 of 21 per cent. This fell to just 16.9 per cent in the past year.

Of all the by-election seats that changed hands in 2025, 88 per cent of them were gains to Reform, Liberal Democrats, Greens, or Others and independents.

Over the past three years a third of by-elections have had an independent on the ballot paper. The analysis says disillusionment with national politics is leading to local-based parties described on the ballot as “… Independents” flourishing in some areas. Candidates that are usually collected in the catch-all category of “others”, contested about one in eight vacancies at the turn of the century but one in four today.