Sep 25th 2021 BERLINERS, MORE than four-fifths of whom rent their homes, have an unusual opportunity on September 26th to vent their anger over the rising cost of housing. A referendum, on the same day as Germany’s national and municipal elections, will give them a say on whether or not the city should in effect “expropriate” some of Germany’s largest residential-property firms, affecting up to 240,000 homes. The vote is non-binding. But its impact on the housing market is already having an effect. On September 17th two giant property investment trusts, Vonovia and a firm it is targeting in a €19.1bn ($22.5 billion) takeover, Deutsche Wohnen, said they would sell…