The series, set in London, revolves around the life of Hannah Baxter (Billie Piper),  a seemingly normal woman, who lives a secret life as a call girl, under the pseudonym Belle.

The series focuses on her professional and private life and its complications as they collide. However, she receives help and advice from her best friend Ben (Iddo Goldberg), in most situations.

Hannah, as the main character, also narrates the series, sometimes through voiceovers but more frequently speaks directly to the audience.

In the fourth season, Belle has a new business proposition, an uninvited house guest in a new home, a challenging client and the all-important question hanging over her head — should she commit to best friend Ben? — Belle's life has never been this complicated.

Secret Diary of a Call Girl S4 starts Friday 24 Feb at 22:30.