T HE OVER-REGULATION of homebuilding in and around thriving cities is one of the great economic-policy failures of recent times. In London the median full-time employee renting the median two-bedroom flat works nearly half the year just to pay the landlord. In San Francisco rent is so high that a four-person household with an income of $129,000 might still qualify for federal handouts. Housing shortages like these have helped suck wealth away from young renters, fuelling tension between the generations. Supply restrictions have a high economic cost—by one estimate, curbs in just three successful cities lower overall GDP in the United States by almost 4%. As more and more voters find themselves on the losing end of property markets, they have also generated a political backlash. In America and Europe politicians are thus under pressure to reduce housing costs.

A rethink of housing policy is certainly overdue. Many of the new ideas are welcome, for example more building and recognition of the harm wrought by NIMBY ism (the attitude of homeowners campaigning against nearby developments). Britain has improved the regulation of rental contracts, a vital component of a functional housing market. Unfortunately, at the same time an old and rotten idea is being resurrected—rent controls. If these proliferate, they will, just like rules that stymie building, skewer property-market outsiders and protect favoured residents.

Across the West rent controls are back in fashion. On September 11th California’s lawmakers passed a bill that would cap annual rent increases across the state at 5% plus inflation. The state is following in the footsteps of Oregon, which earlier this year limited most rent rises to 7% plus inflation. Some Democrats want rents managed nationally. On September 14th Bernie Sanders, a senator and presidential contender, said that the limit everywhere should be 3% or 1½ times inflation, whichever is higher (see article). Meanwhile London’s mayor, Sadiq Khan, has called for rent controls in the capital. Berlin’s legislators have voted to freeze rents for five years from 2020; some German politicians have called for national rent caps. Paris reintroduced rent controls in July, having scrapped them in 2017.