Hopkinson's knowledge of flying led to his strong support for rearmament especially of the Royal Air Force and on 16 November 1938 he declared that the Chamberlain government's inadequate action in that area made it impossible for him to continue to support the government, and resigned the whip. In an article he wrote shortly after, he declared that Conservative Associations should not select "crooks and half-wits" as Parliamentary candidates. However he continued to back the government on the issue of Palestine.