The star, a poster girl for the flat-chested woman, says she doesn’t mind that film chiefs digitally enhance her cleavage on promotional material. But she is furious that sometimes they give her saggy breasts.

The 27-year-old said: “They always pencil in my b****. I was only angry when they were really, really droopy.’

In 2004, Knightley’s bust was digitally enhanced in publicity images for King Arthur in the US but the British posters kept her natural physique. She said: “They gave me these strange droopy ***s. I thought, ‘if you’re going to make me fantasy breasts, at least make perky breasts’.”

Knightley also told US fashion magazine Allure she has a strict “no bottom half” clause when it comes to getting naked on film.

She said: “I don’t mind exposing my ***s because they’re so small — people really aren’t that interested! [But] I think it’s much easier as you get older. You can say,’no’ ‘yes’ ‘no’.”