Supporters fear structure could be torn down as safety hazard and want it to become memorial to postwar foreign labourers in honour of its Turkish creator

Sometimes the currents of history converge in a single spot. In Berlin, one of the most intriguing of those places is a small traffic island with a lovingly tended garden and a ramshackle two-storey structure called the Treehouse at the Wall.

In 1983, Osman Kalin, a Turkish “guest worker”, was looking in his corner of the city cleaved by the Berlin Wall for a patch of earth in which to plant his onions, garlic and cucumbers. Virtually on his doorstep in the Kreuzberg district was a slice of no man’s land next to the concrete barrier and barbed wire. Although it sat in West Berlin, cold war logic meant the lot officially belonged to the communist East.