It was a landslide so large that it even surprised the winner. In last Sunday’s mayoral election in Frankfurt, the Social Democratic Party (SPD) incumbent Peter Feldmann won 70.8 per cent of the vote, against just 29.2 per cent for his opponent, Bernadette Weyland from the conservative Christian Democratic Union (CDU).

This result is even more shocking if you look back six years to the last election. In 2012, Frankfurt’s mayor was the hugely popular Petra Roth, a CDU stalwart who’d led the city for 17 years, and who won her last election with such a massive majority that the SPD didn’t even make it to a run-off. Both Frankfurt’s seats in parliament are held by the CDU – and the CDU has been the largest party on the council almost continuously since 1977. It shouldn’t be easy territory for the SPD, and yet they won every single district.

Map of Frankfurt’s districts, with those won in the run-off by SPD in red. There is no other colour. Image adapted from Wikimedia Commons.

Yet Frankfurt is not an anomaly. Up and down Germany, the SPD and others on the centre-left are winning cities from the CDU, even as social democratic parties continues to sink nationally and internationally. How do they do it, and are there any lessons for British parties?

In 2008, of Germany’s ten largest cities, five mayors were CDU and five were SPD. Now, the SPD hold seven. One (Stuttgart) is Green, one (Cologne) is a pro-refugee independent, and just one (Essen) is CDU.

After Essen, you have to scroll all the way down to Bonn, Germany’s nineteenth largest city, to find a second CDU mayor. The SPD also hold every state capital except Dresden and a majority of Germany’s “Großstädte” (those with a population over 100,000).

The mayor isn’t powerless – although the German title Oberbürgermeister(in) is often misleadingly translated Lord Mayor, the role is comparable to an English elected mayor. The mayor leads the council cabinet, oversees the city’s administration, and acts as its spokesperson. Winning mayoralities matters.

A bit of the SPD’s advantage can be explained by the electoral system. With the exception of the three cities that double as federal states (Berlin, Bremen and Hamburg), most mayors are directly elected in a two-round run-off system: if no-one wins 50 per cent of the vote in the first round, the top two candidates battle it out again a couple of weeks later.

Germany has a fairly fragmented political system – alongside the SPD and CDU (and their Bavarian sister party CSU), there are also the centre-right liberal Free Democratic Party (FDP), the centre-left Greens, the hard left Linke, and recently the right-wing populist Alternative for Germany (AfD), plus a smattering of local parties. Any of these parties can put up a strong showing… but it’s usually the CDU and SPD who end up in the run-off. When push comes to shove, most Green and Linke supporters will take the SPD over the CDU.

Still, the electoral system hasn’t changed in most states in the last ten years, yet the CDU have lost numerous mayoralities in this time.

Frankfurt’s election offers an illustration of how. Feldmann’s campaign hammered home three key policies over and over again: Rent freeze, cheaper transport, free nurseries. (A fourth, “Act ecologically”, was added to posters for the run-off to win over Green voters.)

Weyland by contrast offered a campaign based on identity. “Wer Frankfurt liebt, wahlt Weyland” (“Those who love Frankfurt, vote Weyland”). It’s not that she was without policies – over and over again in debates, she asked voters to read her “Masterplan” for the city – but without simple proposals that could be expressed in a sentence or on a poster, she failed to gain any traction.

Posters for some of the front runners in Frankfurt’s mayoral election (top-to-bottom: SPD, Linke, independent and CDU) Image: Stephen Jorgenson-Murray.

The CDU has an acknowledged “Großstadt-Problem” – they’re losing ground fast in big cities. CDU politicians blame it on the conservative party being too “uncool” for hip city-dwellers, while political scientists Hendrik Träger and Jan Pollex say the CDU suffers from local factors and a selection process that tends to pick unsuitable party insiders. Whatever the reasons, the SPD has managed to sweep through Germany’s major cities.

So is there anything British politicians can learn from Germany – in particular, the SPD’s counterparts in Labour, who lost a string of what seemed like very safe metro mayor elections in 2017?

Personality counts more than party. The CDU has paid the price for putting up a long series of insiders. Here, Labour can perhaps learn from the Tories in the West Midlands. Although the Conservative candidate Andy Street had never held political office before, he narrowly beat Labour’s Siôn Simon, a long-time Birmingham politician.

Other parties’ voters matter. A two-round election – whether Germany’s run-off elections or Britain’s Supplementary Vote system – rewards politicians with appeal outside their base. By winning over supporters of both hard-left and centrist parties in the 2012 run-off, Peter Feldmann went from 6 points behind in the first round to 15 points ahead, securing his surprise election.

Finally, you need clear talking points. When Ben Houchen, the Conservative mayoral candidate for Tees Valley, announced that he planned to bring the failing Durham Tees Valley Airport into public ownership, he was widely mocked. But his airport plan was a concrete proposal – and one that’s very easy to sum up in a sentence – and Houchen went on to secure a real shock victory. Political ideals like patriotism or fairness may go down in a national campaign, but if you’re running for mayor, “Free nurseries” beats “If you love Frankfurt, vote for me” any day.