Piper stars in Secret Diary of a Call Girl , an ITV2 version of Belle de Jour 's The Intimate Adventures of a London Call Girl , a memoir detailing the life of a high-class prostitute . Piper also stars as Hannah Baxter\/Belle de Jour in Secret Diary of a Call Girl , an ITV2 adaptation of Belle de Jour 's The Intimate Adventures of a London Call Girl , a memoir detailing the life of a high-class prostitute .