First, what does it portend about the Liberal Democrats’ prospects of knocking down the Conservatives’ “blue wall”?
Second, what are the implications for relations between Labour and the Liberal Democrats?
At the last general election around four out of every five votes the Conservatives secured in England and Wales came from people who had voted Leave in 2016. Yet the party still managed to win 66 seats where a majority voted Remain.
Despite winning these seats, the Conservative vote fell back – on average by three points. Liberal Democrat support rose, in contrast, on average by 10 points. As a result, the Liberal Democrats won second place in 37 of the 66 seats, Labour in only 27.
Two-thirds of those Liberal Democrat second places were seats – like Chesham and Amersham – in the southeast corner of England. And in line with the pattern elsewhere, the Conservative vote fell back in Chesham at the last election by five points, while Liberal Democrat support rose by 13 points.
In short, Chesham is typical of a clutch of Conservative-held pro-Remain seats in the southeast where the Liberal Democrats had already sown the seeds of a revival and which now represent some of the party’s best chances of making gains at the next general election.
If the party could not do well in Chesham in a by-election, where was it ever going to do well?
Yet the Liberal Democrat campaign was not primarily about Brexit. The party focused on local issues, most notably HS2 and concern about more houses being built locally as a result of changes to planning law.
Indeed, it is very unlikely that the Liberal Democrats’ success was achieved by simply winning over Remain voters.
True, given Labour’s own heavy reliance on Remain supporters, most of the vote the Liberal Democrats gained from Labour (whose voted fell by 11 points) will have come from that quarter.
But even in a pro-Remain seat like Chesham, survey data suggest that only around a quarter or so of those who voted Conservative in 2019 were Remain voters. Even if all of them switched to the Liberal Democrats, they could still only account for around two-thirds of the 20-point drop in Tory support – and in practice the proportion was probably less than that.
This raises questions about how far the result demonstrates the Liberal Democrats’ ability to punch a hole in the Tory blue wall. Although the result may confirm the potential fragility of the Conservatives’ support in some of their traditional southern heartlands, the more the by-election success was the result of local issues, the less likely it is that the outcome is necessarily a portent for what might happen elsewhere.
This suggests that the challenge facing Sir Ed Davey now is to use the by-election success to gain publicity for a message that will appeal more broadly to voters in Conservative-held pro-Remain seats. Otherwise, it could prove to be a victory that is wasted.
Meanwhile, the role that the collapse in the Labour vote played in this election (at 1.6 per cent Labour’s vote fell to a record by-election low), also raises questions about future relations between Labour and the Liberal Democrats.
There is a risk that any post-Chesham revival in Liberal Democrat fortunes may come more at the expense of Labour than the Tories. After all, the polls suggest that both parties are still primarily fishing in the same pond of Remain supporters.
Yet such a development would only increase the Conservatives’ chances of winning the next election – whatever the party might lose to the Liberal Democrats in the blue wall would be compensated by gains from Labour in the “red wall” (and elsewhere).
Unless that is, voters were encouraged or persuaded – as they evidently were in Chesham – to vote for whichever of Labour and the Liberal Democrats look best placed to defeat the Conservatives locally.
There could yet be more talk about the need for a “progressive alliance”.
John Curtice is Professor of Politics at Strathclyde University and Senior Research Fellow, NatCen Social Research and ‘The UK in a Changing Europe’