Kirk's main interests were in foreign affairs and defence, being a British Parliamentary representative on the Council of Europe from 1956 - 1963 and again from 1966 - 1970. He also served on the British-American Parliamentary delegation and various committees of the Western European Union. Having been too young to fight in World War II (although greatly affected by it), he heard Winston Churchill's call for a United States of Europe in September 1946, and devoted much of his career to bringing this about. He was opposed to the British intervention in Suez in 1956, but a strong supporter of Britain's entry into the then Common Market in 1973,and a leading campaigner to keep the country there in the 1975 referendum. A fluent German and French speaker, he particularly admired the way that the Germans had reconstructed their country and developed a peaceful, stable and well-run political system in the aftermath of 1945. At home he campaigned vigorously for the abolition of the death penalty.