In the 1930s Sempill developed extreme right-wing political opinions and was active in several anti-Semitic organizations such as the Anglo-German Fellowship and The Link.
In May 1939 Archibald Ramsay founded a secret society called the Right Club. This was an attempt to unify all the different right-wing groups in Britain. Or in the leader's words of "co-ordinating the work of all the patriotic societies". In his autobiography, The Nameless War, Ramsay argued: "The main object of the Right Club was to oppose and expose the activities of Organized Jewry, in the light of the evidence which came into my possession in 1938. Our first objective was to clear the Conservative Party of Jewish influence, and the character of our membership and meetings were strictly in keeping with this objective."
Members of the Right Club included Lord Sempill, William Joyce, Anna Wolkoff, Joan Miller, A. K. Chesterton, Francis Yeats-Brown, Lord Redesdale, 5th Duke of Wellington, Duke of Westminster, E. H. Cole, John Stourton, Thomas Hunter, Aubrey Lees, Ernest Bennett, Charles Kerr, Samuel Chapman, John MacKie, James Edmondson, Marquess of Graham, Margaret Bothamley, Earl of Galloway, H. T. Mills, Richard Findlay and Serrocold Skeels.
After war was declared Lord Sempill joined the Naval Air Service. Recently released documents from MI5 show that In 1941 Lord Sempill was under suspicion of leaking information to an organized spy ring within the Japanese Embassy.