When Emma Watson expressed an interest in the role, Wenger, Heidi and Goldbacher were delighted. Emma arranged to meet Sandra Goldbacher over a cup of tea, and there was an instant chemistry between them.

"Emma was perfect for Pauline," reports Goldbacher. "She has a piercing, delicate aura that makes you want to gaze and gaze at her." Emma was intrigued by the part; Pauline's experience as a child actress who becomes a movie star had some parallels with her own.

Emma comments: "I was all set to go back to school after finishing Harry Potter but couldn't resist Ballet Shoes. I really loved it; it felt so funny and real. It was also beautifully written." She adds that a scene that had most resonance for her takes place the night before the première of Pauline's first film. Pauline weeps: "Tomorrow night, my face is going to be blown up as big as a house, and everyone will find me out!"

According to Heidi, Emma need not fear. "Emma's performance in Ballet Shoes is a revelation," she comments. "She is maturing rapidly as a young woman and as an actress – her work is sensitive, subtle and intelligent."

Heidi adds: "She is also incredibly hardworking. Our schedule was murderous, and she never once complained, even when she was white with exhaustion." Insiders also noticed a refreshing lack of vanity – Emma agreed to play one scene with her hair in bright blue curlers. "She looked a complete sight but she just got on with it," laughs Heidi.

Nevertheless, Pauline grows into a beautiful teenager in the course of the story, and, when Emma came on set to film her final scenes, she was wearing her first-ever coating of rich, red lipstick. "There were gasps," says Heidi. "We suddenly got a sense of the great beauty Emma is likely to become – and it was breathtaking."