A lot of scenes and dialogue were improvised whilst shooting, with a lot of participation from the actors. The scene in which Mona draws a portrait of Tamsin on the wall of her room was entirely improvised - during Pawlikowski's traveling together with Press, he discovered that she used to do a lot of drawing while she was thinking, so he decided to integrate it into the movie and made a scene out of it.
Tamsin has clearly decided to make Édith Piaf's life even more dramatic than it was. Marcel Cerdan, the boxer, wasn't Piaf's husband. He was her lover, and married, but nonetheless the love of her life. He died in a plane crash and she never recovered from his death. She never killed anyone, let alone with a fork.
Pawlikowski felt Emily Blunt was the perfect choice for Tamsin and that the chemistry between Press and Blunt was perfect right from the start.
Emily Blunt said she shot a scene totally nude on a closed location set, but when she stood by a window, she realized a construction crew was looking up at her.
The whole shoot was done on location in Todmorden during the hottest summer Yorkshire had seen in 50 years.