The Chesham and Amersham by-election result means a party for the Liberal Democrats and a nagging worry for the prime minister, Boris Johnson. But it’s truly devastating for Labour’s leader Keir Starmer.

Looking back at the recent history of British politics, there isn’t anything particularly surprising about the Liberal Democrats taking a seat from the Tories in a London commuter belt by-election. The party long ago mastered the trick of generic opposition, appealing to Left-leaning voters in some areas, and the more conservatively minded in others.

The numbers are impressive – their vote is up 30% from the 2019 general election, to 56%. The Tories are down by 20%. But the Lib Dems’ profile as a party was built up through surprise by-election wins. They’ve learnt how to pour all their national resources into one place, and sink their opponents in a sea of leaflets.

The fact that, six years after the end of the disastrous coalition, they seem to have finally returned to form under Ed Davey’s leadership, is interesting. Clearly, the toxic smell of Tory cooperation has passed, for some voters at least. But it doesn’t mean that the Lib Dems are now about to storm British politics.

For Johnson, it’s a reminder that his 2019 election victory was the product of a particular moment in history and a certain kind of campaign – he successfully waged war on politics, and encouraged people to vote it away. The pandemic has meant that politics has stopped being a dull soap opera, and become once more how we negotiate how we live together, and that’s not great for him.

But it’s also a reminder that his support is built on the chatter of the media. Although much of the press has been snapping at him in recent months because the oligarchs who own our papers hope to replace him with their preferred puppets, he knows they will swing behind his party at the next general election.

Move of the progressives

In the background, it is a reminder of a demographic shift: millennials are moving out of London and into commuter towns that circle it, and they aren’t becoming Tories as they go. For a generation whose life experience has been shaped by Iraq, the 2008 crash and climate breakdown, austerity and the housing crisis, the traditional move out of town when you have kids may be happening, but the corresponding shift to the Right doesn’t seem to be.

In the recent local elections, seats across the south of England started to slip from the Tories’ grasp, just as they were winning councillors in the north. In Oxfordshire, where I lived for most of the 2010s, the Conservatives lost control of the county council for the first time ever, replaced by an alliance of Labour, Lib Dems and Greens.

But this didn’t surprise me. In the past few years, my friends have been moving out of the traditionally red and green east Oxford, with its overheated housing market, and into the more affordable towns surrounding the city, taking their progressive ideas with them. Where Hartlepool has been abandoned by its youth, they’ve moved to towns such as Amersham. But while the Tories will be keeping an eye on this trend, they probably aren’t overly concerned.

In contrast, the result is a serious worry for Starmer. As the polished opposition leader sinks like cement in the polls, his friendly pundits have insisted that Johnson is using syringes as political pogo sticks, and enjoying a vaccine bounce. There is nothing he could have done differently, they insist. Whether he has done anything at all is the better question.

Starmer has already secured the wrath of much of his membership. He appears to have run to the Left in the leadership election, then side-stepped to the Right. The result last night punctures the idea that Johnson is unassailable. If the Lib Dems can do it, why can’t Labour?

Labour may be ignoring the 1.6% they got in the by-election, that they came in behind the Greens, on 4%, and that this was the party’s worst result in modern history. But if they lose the Batley and Spen by-election in West Yorkshire on 1 July, as they lost in Hartlepool last month, then Starmer’s leadership will struggle to survive another year.