Last night Labour held Stoke Central and lost Copeland to the Tories. As usual, by-elections don’t tell us a huge amount about the bigger political picture, but are very important in setting the political narrative.

By-elections are very unusual beasts. Because they don’t decide who will form the government for the next five years, only who will be the local MP, people are comparatively free to use them to register a protest. They are much more fiercely contested than your average seat at a general election. The constituency itself will also normally have its own local ideosyncracities that mean it can’t just be read as if it is a microcosm of Britain as a whole. So when people ask me what by-elections tell us, I normally say not much: if the change in the vote is in line with what the national polls are showing then it tells us nothing we didn’t already know, if the change is different to the national polls it’s probably just because by-elections are very different to general elections.

Looking at the two results, Copeland is a marginal seat between Labour and the Conservatives… albeit, one that had been in Labour hands for eighty years. The national polls tend to show the Conservatives about 14 points ahead of Labour, the equivalent of a 3.5% swing from Labour to Conservative since the general election. Therefore if Copeland had behaved exactly in line with the national polls it should have been on a knife edge between Conservative and Labour. In the event the Tories gained it comfortably. We cannot be certain why the Tories did better than the national picture would have predicted, thought the most obvious hypothesis is the unusual nature of the seat: Whitehaven is a town wholly dominated by and dependent on one industry – nuclear power – and the Labour party were perceived as being hostile towards it.

On the face of it Stoke Central was a less interesting result – Copeland is one for for the record books, but Stoke saw hardly any change since the general election (only the Lib Dems really saw a significant increase in their share). However it does perhaps give us a idea of the limits to the UKIP threat to Labour. UKIP were perceived as the main challengers from the beginning and it was a promising seat for them: a somewhat neglected working class Labour seat that voted strongly for Brexit, but with a Labour candidate who was remain. They seem to have thrown all they could at it, but with very little success. Again, we can’t be certain why – Paul Nuttall obviously had a difficult campaign and anecdotally UKIP’s ground game was poor, but there are also wider questions about UKIP’s viability now Brexit has been adopted by the Conservatives and without Farage at their helm. By-elections have often been an important route for smaller parties, getting them publicity and a foothold in Parliament. Whenever there has been a by-election in a northern city in the last five years or so there has been speculation about it being a chance for UKIP, but they never seem quite able to pull it off.

So what will the impact of these by-elections be? Copeland will be a body blow to Labour simply because of how incredibly unusual it is. Governments do not normally gain seats at by-elections. Lots of people will be writing about past examples today – 1982 in Micham and Morden (Lab vote split because of SDP defection, and the government got a surge of support during campaign because of the Falklands); 1961 Bristol South East (Tory gain only because the candidate with the most votes – Tony Benn – was disqualified for being a peer), 1960 Brighouse and Spenborough (ultra marginal to begin with). The fact that one has to go back that far to scrape a few examples that generally have extremely unusual circumstances underlines how freakish this is. The political narrative will go back to how Labour are in crisis…but whether that makes the slightest practical difference, I don’t know. Might it provoke another Parliamentary coup within Labour? Who knows. Might it sow some doubts among Corbyn supporters within the Labour party? Again, who knows. The point is, Labour have had terrible poll ratings for a long time, Jeremy Corbyn has has terrible poll ratings for a long time, but this did not stop him being being relected leader last year. The question of Labour’s leadership is one that seems to be a lot more about the opinion of Labour members than the wider public.

After every by-election I write pretty much the same blog post. By elections tell us almost nothing about the state of public opinion, but are nevertheless extremely important in setting the political weather. This one is no different.

First, why they don’t tell us much. By elections are not little mini general elections. They take place in but a single constituency, which is not necessarily representative of the country as a whole. Richmond Park is an extremely affluent slice of South West London – it is not like other places. In a by election that it appears the Lib Dems successfully steered onto the issue of Brexit it is wildly unrepresentative – on Chris Hanretty’s estimates it voted 72% to remain, making it one of the thirty most remainy constituencies in Britain (and the fourth most remainy out of the 330 Tory constituencies). Secondly, by elections don’t change the government. In a real election the public are heavily influenced by issues like who they trust to run the country, who will the best PM. By elections don’t change that, so there are different dynamics. Thirdly, the intensity of campaigning is different, so larger swings are common. Campaigning was a particularly unusual issue here because Goldsmith was running as an independent – while some conservative MPs came to help him out, he did not have the might of the Conservative party machine behind him, while the Lib Dems appear to have thrown the kitchen sink, worktop, cooker, etc at it.

So it’s an unusual event in an unusual area that, in isolation, tells us little. It does, however, serve as an illustration of a wider pattern we’ve been seeing in local government by elections, where the Lib Dems have been doing very well. Lib Dems always out perform in local by-elections (and simplistic analyses of them has long been a straw for their supporters to grasp in dark times) but even by their own high standards they’ve been pulling out very positive results that have not been reflected in national polling. My best guess is that the explanation for this is something along the lines of people having stopped wanting to punish the Lib Dems. Having seen them humiliated and almost wiped out of parliament, they think they’ve had their medicine and now when a nice Lib Dem candidate comes along in a by-election people are again willing to give them a hearing. They aren’t doing well at a national level because people don’t hear them – they are the fourth party in votes and seats and struggle to get much coverage.

The impact of this victory will, therefore, be important. It will get the Lib Dems a hearing, remind people they are there and can win. Expect to see a Lib Dem boost in the national opinion polls, like they enjoyed after by-election victories years ago. The Lib Dems have a long history of using by election victories to show they are a viable party and to get themselves noticed. This could be another.

There’s another important impact too, that on the crude Parliamentary maths. Theresa May had a majority of 12, now it’s 10. As that is whittled away defeats become more likely…and an early election becomes more likely. The by election tells us little about what would happen in such an early election. Richmond Park is an extremely pro-EU seat, while a general election would be fought in a country that voted for Brexit. More than three-quarters of Conservative seats voted to Leave (and most those those that didn’t were far closer than Richmond Park). Don’t imagine that the swathe of Lib Dems seats the Conservatives won in 2015 are all itching to go back to the Lib Dems purely on the issue of Brexit – looking at Hanretty’s estimates, 20 of the 27 Lib Dem seats that the Conservatives gained in 2015 voted to Leave the EU.

Previous polling has suggested that the Lib Dems could indeed do very well in an early election fought around the issue of Brexit, and I think that is the case (especially if they are the only explicitly pro-membership party and can win pro-European support from Labour). Nevertheless, those same polls also suggested a very solid overall win for the Conservative party. Britain is NOT just a bigger version of Richmond Park.

Today is the Rochester and Strood by-election. After every by-election I see the same questions and I write essentially the same post. Given that, I thought I might as well write it before the result: whatever happens in the Rochester and Strood by-election it won’t tell us anything we didn’t already know about public opinion.

By-elections are very unusual beasts. They are fought with huge intensity and media attention, but with very little direct consequence – the government will still be the government the next day, it’s only one single seat that can change hands. They also often have unusual local circumstances – in this case a defecting member of Parliament. When a by-election behaves in line with the national polls, it doesn’t tell us anything we didn’t already know. When it behaves differently to the national polls, it’s probably because of the unique factors of by-election.

Assuming that the by-election polls from Ashcroft, ComRes and Survation are all correct and Mark Reckless wins tonight’s by-election we’ll probably see lots of comments tomorrow about UKIP doing well and being a threat to the Conservatives. I’d also expect lots of comments about how Labour didn’t win when they should have. Plus perhaps some comments about the derisory vote the Lib Dems will almost certainly get. Perhaps they’ll finish behind the Greens or even the Loonies or random independents.

To take those one at a time, UKIP are not likely to do as well nationwide in a general election as in a by-election where they have an incumbent MP, so this won’t tell us anything about their likely level of support come the general election – nor will it help answer the question of how concentrated their vote will be, and how well it will translate into returning MPs to Westminster. In terms of Labour, this is the sort of seat that an opposition doing really well in the polls and headed for a landslide win could reasonably expect to win… but we don’t need a by-election to tell us that Labour are not soaring ahead in the polls, and are not currently in a position that would translate to a landslide win. We already know that they are struggling to maintain first place in the polls and are seeing the anti-government vote split between them and other parties. As for the Liberal Democrats, the embarrassment of finishing lower than 4th place and losing their deposit is no longer anything new for them and doesn’t tell us anything new about the dire straights they find themselves in.

The other thing I invariably say after explaining how by-elections tell us virtually nothing about wider public opinion is that it doesn’t make the result any less important. A lot of politics is about the press narrative, about Westminster personalities and morale and in all those senses tonight’s result really does matter – if UKIP do really well it should keep UKIP’s momentum rolling, help them persuade voters they are a viable choice at the election. Perhaps we’ll see them get a boost in the polls from the publicity. Perhaps it will give the Conservative party’s morale a knock, perhaps encourage another defection(s) and turn the media pressure back onto David Cameron after an unpleasant few weeks for Ed Miliband. By-elections are very important – but because of their effect on the narrative, not because they really tell us much about wider public opinion.