After briefly working for the British consulate in Seville, he joined the Red Cross on the Italian front, and was involved in the Battle of Caporetto in which the Red Cross lost 80 of its ambulances. Following the end of the war, he took a post as assistant to the Governor of Fiji. He eventually returned to London, and worked at Selfridges in Oxford Street, soon becoming private secretary to Gordon Selfridge. After Selfridge's wife and mother both died, Dunstan became a close adviser, living at Selfridge's house in Lansdowne House on Berkeley Square at a time when the store was the most popular and successful in the city.