The only part of the British Isles that can answer the question 'What was it like to be invaded and occupied in World War 2?' are the holiday islands of Jersey, Alderney, Guernsey and Sark. Left undefended in 1940, they fell like ripe plums into German hands. Thereafter they were turned into the most heavily defended parts of the Nazi Atlantic Wall, with massive fortifications, gun emplacements and underground storage tunnels. An army of foreign...