One reason why scholars of the humanities find their subjects attractive is that they can escape the tedium and compromises of the everyday. A historian can spend much of his lifetime among the peasants of a medieval Languedoc village without ever having to get his feet muddy or stagger out of bed before dawn to milk the cows. A philosopher can immerse himself in the formal logic of possible worlds, only surfacing when necessary for tea and a pot noodle. But many art historians, simply by virtue of years spent scrutinising a painter’s work, are drawn into the glamorous, shadowy, viperish milieu of the art market. Here, they are flattered and cajoled by collectors and dealers, curators and auctioneers, who lubricate positive attributions with sumptuous hospitality and plumped-up expenses. If they don’t deliver the expected judgements, they can find themselves abused and ostracised, or even threatened with libel actions, to guarantee their silence.

Martin Kemp is one of the good guys. The pre-eminent Anglophone scholar of Leonardo da Vinci, he carries himself with saintly phlegmatism in the face of mockery, apoplectic tirades and legal threats from disappointed owners of pretenders to the da Vinci oeuvre. With Robespierrean rectitude, he declines any emolument.