It was only natural that Barack Obama and David Cameron should have read Nudge and loved it. What could be more alluring to a politician than a book full of recipes for turning sceptical voters into allies?

Published in 2008 by economist Richard Thaler and law professor Cass Sunstein, Nudge used the insights of behavioural economics about how unreliable and irrational people’s choices are. It suggested ways to coax people into doing what was best for them – displaying bananas more prominently than biscuits in school cafeterias, say. “Choice architecture” was a hit. The US president hired Prof Sunstein, his old friend, as a senior regulatory adviser for a time. The UK prime minister fell hard for the concept, consulting Prof Thaler and setting up a Behavioural Insights Team.

But this system of “libertarian paternalism” is ambiguous, and its record mixed. Maybe its libertarianism part will rally the public behind a new vision of 21st-century government. Maybe its paternalism will strike its target audience as not just bossy but sneaky, too. US state schools, at the instigation of the federal government and with the blessing of Michelle Obama, are offering healthier lunches, but the kids cannot stand them. Bureaucrats recently beat a humiliating retreat back to peanut butter sandwiches. In Britain, the “Nudge Unit” has solicited organ donors at driving licence renewal time. But much of its work involves new ways to shake people down. When a request for unpaid car taxes is accompanied by a photo of the car, delinquents snap to attention.