FEW places, in 1899, better encapsulated Britain’s industrial pomp than Oldham. Its skyline was the Manhattan of its day: a forest of smoke stacks emanating from the cotton mills, the Pennine hillsides freckled with mansions housing the country’s largest concentration of millionaires. So when the Liberal Party swept aside the Conservatives in a parliamentary by-election there—after a campaign that had turned on church funding, women’s suffrage and trade unionism—it rattled windows down in London. Winston Churchill, at 24 one of the two Tory candidates, compared the experience to discovering that a bottle of champagne had been left uncorked for a night and had gone flat (in short: it was a considerable trauma). The upset illustrated the Tories’ loosening grip on the establishment and thus foreshadowed the Liberals’ landslide victory of 1906.

Today, once more, Oldham is a battlefield on which an early, indicative skirmish in a larger political war is unfolding. As in 1899, the Lancashire town is holding a by-election after the death of one of its MPs, but today this erstwhile bellwether for the high-Victorian bourgeoisie is a microcosm of forces acting on Europe’s social democratic parties. With its large blue-collar workforce it has been a Labour Party bastion for 68 of the past 70 years, the party’s dominance surviving Fordism’s long twilight, the arrival of Pakistanis and Bangladeshis in the 1970s and race riots in 2001. Now, however, ahead of the vote on December 3rd, Labour’s electoral coalition is being torn apart by the anti-immigration UK Independence Party. With its purple UKIP yard signs, its rusting factories and its shops selling halal meat and salwar kameez, the Oldham West and Royton constituency stands for political fractures in old working-class areas across the continent.

For much of its 22-year history UKIP has chipped away at the right flank of the Conservative Party, first in its Home Counties heartland and then in working-class southern seats like the two it prised from David Cameron’s hold at by-elections last year. But the general election in May marked the arrival of a new phase: UKIP held only one of those seats and came second in 120 others. Of these, it looks most threatening in a string of formerly uncompetitive Labour strongholds outside big northern cities; its vote share in Oldham West and Royton, for example, rose from 3% to 21%. A party once confined to the comfortable gin-and-jag belt around London is now a serious presence in the bitter-and-bus-pass belts around Manchester, Sheffield and Newcastle.

There the election in September of Jeremy Corbyn, a hard-left London MP, as Labour’s leader has been a tremendous boost for UKIP—and its candidate in Oldham, John Bickley. The scene: a street of semi-detached houses built for workers at the now-closed Avro factory that once made the Lancaster bomber. Arriving home, a resident in a high-vis jacket confesses that he is Labour by habit and UKIP by preference. “He’s an idiot,” he adds matter-of-factly of Mr Corbyn: “his foreign policy is totally out of date.” A couple of houses down an old man in a vest declares himself a convinced socialist, a scion of a “strong army family” and utterly alienated by the unwillingness (as he sees it) of Mr Corbyn, a unilateral nuclear disarmer, to defend Britain. “I call it the political version of the Stockholm syndrome,” says Mr Bickley. “I am putting out a hand [to Labour voters] and saying: you can leave your captor and come to a safe place.”

Excessive this may be, but playing out on the streets of Oldham is a story repeated across Europe; a suspicion of political elites borne of stagnant living standards, doubts about globalisation borne of deindustrialisation and in particular hostility to immigration borne of shifting demographics and pressures (however unrelated) on housing, wages and services. Support for nativist parties, ranging from Britain’s blokeish UKIP to France’s hard-right National Front and Hungary’s overtly racist Jobbik, is squeezing traditional social democratic parties more comfortable discussing redistributive social policies than flags, nationhood and identity. UKIP plans to squeeze Labour hard on this in Oldham, concentrating its campaign on immigration, defence and Mr Corbyn’s obvious ambivalence towards patriotic symbols from the armed forces to the royals.

A wilting rose

The by-election is especially representative of the bigger picture because each of the main candidates epitomises his own side’s best hopes. Mr Bickley, the son of a trade unionist, entered politics only two years ago (aged 60) and deals in pub aphorisms—on everything from climate change to the Middle East—that resonate with locals. It is hard to imagine a figure better able to connect with the disillusioned, older voters who may decide the by-election. Meanwhile Jim McMahon, his dynamic Labour rival, is about as optimistic an embodiment of his party’s prospects as it could wish for. The son of a truck driver who left school at 16, he runs Oldham’s innovative, well regarded council at just 35 and has close links to the armed forces. (Two months ago Bagehot committed to this page the hope that Mr McMahon’s professed indifference to the national stage was merely false modesty.)

The result is something like the ultimate contest between social democracy and the populist forces threatening it across Europe. If Mr Bickley can defeat as forward-looking an example of the mainstream centre-left as Mr McMahon (or even limit him to a narrow win), Labour should be terrified for its strongholds across the English north, and thus its prospects of winning a majority any time soon. Its counterparts from Malmo to Marseille should be similarly worried. But if Mr McMahon scores a clear victory, Europe’s social democrats should promptly seek to learn from his achievement. What happens in a rainy town in Lancashire next month will give the continent’s embattled left-wing moderates—not to mention its surging populist parties—a glimpse of their future.