Riddles began his career as an apprentice at the Crewe Works of the LNWR. After serving as a Royal Engineer duriong the Great War, Riddles returned to LNWR and in 1920 was appointed the assistant to the works manager. In 1928 he transfererred to Derby to work as assistant works suerintendant, working for H G Ivatt; and then, in 1933, he became locomotive assistant to the Chief Mechanincal Engineer. Having worked for the Ministry of Supply, where he became Director of Transportation Equipment, during the war, Riddles returned to LMS in 1945 and was given the position of Vice-President.. Later, in 1947, he was appointed Chief Mechanical Engineer of British Railways , and eventually retired in 1953.