Cities around the globe are facing a stark reality: There are not enough affordable places for people to live. Housing in most big urban areas is now considered out of reach for the average worker, fuelling a growing sense that a decent home has become a privilege traded among the “haves”, impoverishing the “have-nots”.

Thorny questions abound: Should new luxury apartments in London – many owned by foreigners – be allowed to lie empty, while thousands of people sit on waiting lists for affordable homes? If migrants streaming into Beijing for a better life turn to dangerous, illegal dwellings, where will they go when those places are demolished?