What council by-elections tell us about the changing political system
Welcome to the 194th edition of The Week in Polls (TWIP), which takes a look at trends from the last half-year of council by-elections.
That is followed by a summary of the latest national voting intentions polls, seat projections from MRPs, and the most recent party leader ratings.
Subscribers who pay for the full edition can also read a set of ten insights from the latest polling and analysis, including:
Public opinion on the idea of banning trail hunting;
Which news stories people actually noticed in 2025; and
What drives support for Scottish independence.
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And with that, on with the show.
Goodbye, old two-party system?
The overall picture of council by-election results1 continued a familiar pattern in the last quarter of 2025: Reform making big gains, the Lib Dems also progressing, the Greens inching forward but not surging as in the national polls, and both the Conservatives and Labour plunging:
This pattern is why on many a Friday, after that week’s council by-election results are in, you will find me making a comment on social media such as:
This is, of course, at odds with the story being told about national politics. The standard story there is about political fragmentation and the rise of five/six party politics that may even break first past the post come the next Westminster general election.
A more sophisticated and increasingly popular version of that story is to view British politics as being a contest of two blocs, a left/liberal one and a right/populist one, with little movement of voters between the two blocs. Rather, there is plenty of competition between the parties within each bloc and a race also for each bloc to be the best at raising turnout of its own supporters.
The relevance of council by-elections
So let’s dig further into what is happening in council by-elections. Following these contests is not an alternative, and certainly not a superior alternative, to following national voting intention polls. But it is a useful supplement because, as well as their own inherent importance in electing people who make decisions about housing, adult social care and more, such contests also help illuminate the political tides that are influencing national party standings.
Moreover, where the pictures differ between national polls and local by-elections, they provide useful small warning signs about how the polls might be erring. For example, the continued muted nature of the Green Party performance in council by-elections is a helpful hint that those national polls showing the Green Party having surged the most are perhaps less likely to be right than those national polls showing a smaller rise in Green support.
Council by-elections since May
For the following results, I have looked at all the council by-elections in 2025 since the May round of elections (i.e. since the big Reform surge), and the results include elections that were deferred from the scheduled May elections due to the death of a candidate. For the small number of by-elections where more than one seat was up, I have only counted them once for this analysis. Thank you to John Swarbrick for providing the underlying data. It adds up to just under 200 contests in all.
You can see the seat changes over on my website but here I am going to look into the pattern of party contests. Let’s start by looking at how often each party finished in the top two in each ward, comparing the result prior to a by-election with the by-election result itself:
As you can see, in nearly two-thirds of the seats with by-elections, the Conservatives had previously finished in the top two (65%), but in the by-elections they only finished in the top two just under a third of the time (32%). For Labour, there was a similar plunge, while Reform leapt into being one of the top two finishers nearly three-quarters of the time.
For the Liberal Democrats, and to a smaller extent for the Greens, there has been growth in how often the parties are in the top two. This means that seat growth for the Lib Dems has not simply come from the party mopping up where it was already strong; rather the party is getting into contention, and sometimes winning, seats where it was previously not in the top two.
Overall, while the top two parties had previously been Conservative and Labour in 29% of wards, only 2% of by-election results saw those two parties as the top two finishers. (Yes, 2%.)
While in nearly nine out of ten cases (89%) at least one of Conservative or Labour had been in the top two, when the by-election results are tallied, it was only 54%. Or in other words, in nearly half the by-election results (46%), neither Labour nor the Conservatives were in the top two.
By contrast, while Reform had not been in the top two in 95% of cases (often due to not having stood a candidate), in the by-election results it was one of the top two finishers in 70% of cases.
Who is challenging Reform?
But if by-election results have become very much a case of Reform versus someone, who is the someone turning out to be?
Most frequently, in just over a third of all contests where Reform finished in the top two, it is the Liberal Democrats who were the other top two finisher. That is a big switch from only 1% of the results in these wards having previously been Reform/Lib Dem top two pairings.
So it is now more common for Reform and the Lib Dems to be the top two than it had previously been for Conservatives and Labour to be the top two. Even though it should be noted that having a third of contests seeing Reform and the Lib Dems comprising the top two is still a minority of contests, that is quite the shift.
How the blocs are faring
One thing, however, is barely changed in these by-elections.
In the by-elections, in 56% of the results there was one party from the right/populist bloc and one from the left/liberal bloc in the top two. In the prior results in those wards it had been 57%.
In both cases that is over half, and so in that sense thinking of politics through the two-bloc prism makes sense. But also that proportion is not growing, which adds a note of caution on going to town on using the two-bloc model to understand where our politics is heading.
A sign for the future?
Whatever your preferred way of looking at politics, with only 2% of by-elections producing a Labour/Conservative top two combination, that old party prism is being weekly contradicted by how people are voting in council by-elections.
Of course, that does not make council by-election results predictive of future council results, let alone general election results. But the changing political patterns of contestation in them is a sign of where things may be heading in those other contests too.
Elsewhere from me…
If you spot a factual error…
Borrowing an idea from Stuart Ritchie and others, if you spot a factual error in an edition of this newsletter, I will give you a 12-month free subscription to the paid-for version (or an extra 12 months on your existing one). Factual rather than grammatical errors, and factual errors rather than disagreements over interpretation, qualify, with my decision being final. Messages about both of those are always very welcome, though.
Voting intentions and leadership ratings
Here are the latest national voting intention figures. Very wisely, pollsters have not since last time given us any recent voting numbers to mull over (though there is the More in Common MRP). But not long to wait until we find out if those two most recent three point drops for Reform are just a bit of noise or a trend:
The table is also online here. It is updated regularly through the week with new polls.
Next, the latest seat projections from MRP models and similar models, also sorted by fieldwork dates. As these are infrequent, note how old the ‘latest’ data is. There is this time a new MRP from More in Common, though note that as they say, “there is one major caveat: tactical voting. For the first time we have explored how tactical voting could reshape the model projections”. In other words, the impact of tactical voting is, to a significant extent, something that they look at in addition to their model’s figures shown below. More details here.
Finally, a summary of the latest leadership ratings, sorted by pollster name and with a little bit of new data this time around:
The table is also online here with additional details, and is updated regularly through the week as new data comes out.
For the historic figures for both voting intention and leader approval, including Parliamentary by-election polls, see PollBase.
Catch up on the previous two editions
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What people think counts as ‘Britishness’, and 9 other polling insights you shouldn’t miss
The following 10 findings from the most recent polls and analysis are only for subscribers who pay for the full edition, but you can sign up for a free trial to read them straight away.
The Guardian reports that “The number of people who believe ‘Britishness’ is something you are born with has almost doubled in two years, according to
