A glimpse of Roald Dahl’s adolescent correspondence and childhood is all it takes to recognise a born writer. In their elegant script and with their impressive respect for the niceties of spelling and grammar, his letters home, signed ‘Boy’, display a descriptive flair, a delight in vocabulary and a relish for the unusual. Nor is there any question about his acuity: according to family legend, the first utterance by the infant Roald was, in Norwegian, ‘Daddy, why aren’t you wearing your slippers?’

Dahl’s genius was based on his ability to re-enter the mind of a child, to shock and to scare while rendering with wit the macabre and the disgusting, and to stretch both his and our imaginations so that the mundane might become wondrous. On a corridor wall at