Billie Piper has dismissed rumours she's planning to return to sci-fi series Doctor Who - but confesses she may make a surprise return one day. The actress bowed out of the show after 27 episodes as the Doctor's assistant Rose Tyler. The show has kick-started Piper's big screen career - she is currently starring as a London prostitute in TV movie Secret Life Of A Call Girl. The 24-year-old has no plans to go back to the sci-fi series, and is baffled by recent claims she is lining up a return. She says, "A friend of mine told me he'd read about that. It's news to me. I think I'd find it very hard to play Rose Tyler again, but I don't rule out a return to the show in some form or another at some point in the future."