Following the Irish War of Independence, Clarke returned to the Ministry of Health and while there was knighted in 1923 for his services in Ireland. But the same year he was made redundant as part of the Geddes Axe. In 1924 he established Editorial Services Ltd, now generally seen as the first UK public relations agency, and by the end of the 1920s he was running a significant operation with 60 staffers. Its clients included Heinz, Lyons and the National Union of Teachers. While running Editorial Services Ltd, he developed the world's first public relations code of conduct and he championed ethics in public relations.