Hannah Baxter (Billie Piper) is the lead semi-fictional character and protagonist of the British ITV2 television series Secret Diary of a Call Girl.

Hannah secretly has a double life as a high-class call girl as her alter ego Belle, for which she acknowledges and comments directly to the audience, throughout each episode.

The character Hannah Baxter is based on the real life published memoirs of former London call girl Dr. Brooke Magnanti, who is better known by her pseudonym, "Belle de Jour".

A university graduate with a degree in English literature, she chooses a career as a call girl for the sake of the money; she reveals that she makes a yearly turnover of £105,000 (though, she claims, it takes £20,000 "to be Belle").

[2] She further claims her career is ideal since she is "fundamentally lazy", in control, and also because she genuinely enjoys the pleasures of sex (in a video blog she reveals with some degree of satisfaction that she lost her virginity to her 40-year-old chemistry teacher[3]).

Open minded and truly a professional when it comes to her role as a high end prostitute, Hannah has gone as far as considering a breast augmentation to better appeal to clients, and will likely attempt a variety of fetishes and bedroom scenarios with them.

Furthermore, Hannah wants to pride herself on her skills in the bedroom and her ability to size up her male clients, such as predicting what kind of lifestyles they lead based on what their sexual interests are and the price, ratings, and styles of the hotels they pay for on "out calls".

Despite Hannah's discretion and lengthy attempts to keep both worlds apart, the issue of secretly juggling both identities frequently reoccurs in the series, often resulting in negative inner turmoil for her and feelings of loneliness.

Although Ben is disappointed and angered that she has been deceiving him, he accepts Hannah's choices, counsels her on matters of work, and even joins a foursome with her and a married couple who are her clients.

Towards the end of the season Hannah is offered a role as a courtesan[clarification needed], which she is initially enthusiastic about, but eventually walks away from – despite the luxury – because of the lack of excitement.

[6] During the first three seasons, Hannah lives at flat 23 somewhere in Stephenson Street but the exterior was near the Trellick Tower in Kensal Town in the Royal Bourough of Kensington and Chelsea.

During the second season, Hannah considers breast augmentation done by her client, David, who is assisted in his office by nurse Elena (played by Lynsey Pow).

With the support of Ben and Bambi, Hannah writes and publishes a memoir of her adventures and life as London call girl at the end of the series, where she – under disguise – remarks to an interviewer on television that she had once been in love, referring to Alex.