The three youngest Mitford sisters — Unity, Jessica and Deborah — used to fantasize in their schoolroom about what they would do “when they grew up”.

Jessica, known as Decca, planned to run away and be a communist; Deborah, known as Debo, dreamed of marrying a duke; and Unity longed to go to Germany to meet Hitler. As Jessica wrote in her memoir, Hons and Rebels: “Seldom have childhood predictions materialized with greater accuracy.”