Early on the morning of Good Friday 2008, John Berger made his way to the National Gallery in London to look at the Crucifixion by Antonello da Messina. It’s one of six versions the Sicilian painted, and the least allegorical rendering of the biblical story Berger knows: ‘the most solitary painting of the scene’. Standing in the gallery, sketchbook in hand, the writer was approached, he tells us, by ‘an armed security guard’ who objected to the placement of Berger’s shoulder bag on a gallery assistant’s empty chair. An argument ensued and Berger began to swear; he was marched to the exit and summarily deposited in Trafalgar Square. This is a curious anecdote, to be sure – are there armed guards at the National Gallery? – but a reminder too (through both the tale and its telling) that the ornery, eloquent and oracular critic has always been, perhaps above all, a performer.