The idea of guaranteeing a basic income for everybody has many obvious flaws but one overwhelming virtue. It enshrines the principle that every citizen is a valued member of society and has a right to share in its collective wealth.

That conviction has animated radical thinkers for 500 years since the argument was first sketched out in Sir Thomas More’s Utopia. The idea has gained renewed resonance in our own times as we fret about the erosion of living standards, the concentration of wealth and the possible threat of mass unemployment caused by technological change.

But for half a millennium universal basic income has remained little more than a utopian dream because it has always crashed up against the rocks of reality. The chief objections are ones of principle and practicality, encapsulated in two questions.