The National Gallery has ruined Christmas. Or, to be more precise, it has had a very good go at wrecking one of the world’s greatest Nativity paintings. The fact that Piero della Francesca’s Nativity is back on view for the festive season, after a three-year restoration the London gallery vaunts as careful and revealing, should be glad tidings. But my joy turned to ash when I saw it. What in the name of God inspired the restorers to paint two completely new and distractingly moronic shepherd’s faces? Or a big white blob on the stable wall?

The Nativity, a mysterious and elusive work of haunting wonder, has been, oh so carefully and responsibly, rendered clumsy and plodding, if not downright comical. Almost every colour has been altered, every line re-emphasised. It’s like a garish digital reconstruction of what the painting may have looked like in 1475 when it was new – except, instead of offering this as a hypothetical, it has been physically repainted or, in the evasive language of restorers, “retouched”.