Saving Mr Banks hits cinemas this weekend so, in the spirit of all things supercalifragilisticexpialidocious (and breathe) Victoria Coren Mitchell explores the dark and complex life of writer PL Travers, revealing her 20-year battle with Walt Disney and how the big screen adaptation overshadowed her writings but made her rich. Emma Thompson and Cameron Mackintosh are on hand to help Victoria get the inside track with just a spoonful of sugar to help the medicine go down.