His Own Executioner: The Life of Nigel Balchin by Derek Collett SilverWood, 2015, 455 pages, £11.99   Between 1942 and 1945 Nigel Balchin (pronounced bol-chin) wrote three novels that propelled him into the ranks of the top British novelists: Darkness Falls from the Air, The Small Back Room and Mine Own Executioner. They broke new ground in putting the hero’s day-to-day work at the forefront of the action: respectively, a senior public servant trying to co-ordinate industrial production in the early stages of the war; a scientist in wartime weapons research; and a psychiatrist practising without a medical degree. Slightly…