Sempill faced questioning after his return from Japan and again during the 1920s and 1930s. An encounter concerning the Blackburn Iris led to an admission that he had broken the Official Secrets Act, yet the response remained a warning. Protecting the establishment from embarrassment and protecting access to Japanese diplomatic ciphers both discouraged prosecution. He subsequently represented Mitsubishi in Europe from 1932 to 1936 and held senior positions in the Royal Aeronautical Society. Foreign aviation visits and later Admiralty employment continued to give him access to technical information despite those earlier concerns.
Notable Point · 29:59-32:33
Sempill keeps aviation access despite repeated security warnings
Repeated investigations failed to end Sempill's access to aviation information, while prosecution risked exposing diplomatic codebreaking.