“In December 1920 Father Christmas wrote a letter to a modest house in the Oxford suburbs, enclosing a watercolour sketch of his own rather more exotic domed snow house, approached by a flight of steps lit by ice lanterns. ‘I heard you ask Daddy what I was like and where I lived,’ he wrote to three-year-old John Tolkien, and as the family grew to four children, he continued to write every Christmas for 23 years, until the youngest, Priscilla, was 14.”