When does Secret Diary of a Call Girl return?

Secret Diary of a Call Girl is a British drama television series that aired from 27 September 2007 to 22 March 2011 on ITV2. It is based on the blog and books by the pseudonymous Belle de Jour. The series, set in London, revolves around the life of Hannah Baxter, a young woman who lives a secret life as a call girl.