A listener of the show/podcast from countries that used to be part of the British Empire, such as the United States of America. The term was in use particularly around the time of the release of the film "The King's Speech". It was pointed out that there is great entertainment in seeing a member of the Royal Family interacting with a commoner (as also seen in "Mrs Brown" starring Judi Dench and Billy Connolly).
And as they always say, "there's no commoner commoner than a colonial commoner." This, however, may not be true. According to Boaventura de Sousa Santos, a left wing professor of sociology from Brazil, "The fact that the colonizer was colonized in turn does not mean that he was better or more closely identified with those he colonized. Nor does it mean that those colonized by a colonized-colonizer are less colonized than those colonized by a full-fledged colonizer" Therefore, you can indeed get commoner than a colonial commoner if you are a colonial commoner colonized by a common colonized colonizer! (Or 6C for short)