Keira Knightley is wary of exposing her body on film.

The actress, who has posed nude in Chanel perfume advertisements, is more modest when it comes to movie roles.

She said: "I have turned roles down because I thought that the sex and nudity was explicit — I'm not interested in that."

Knightley has, however, dared to go bare for intimate scenes in her new film, 'The Duchess', in which she plays Georgiana, the Duchess of Devonshire.

The film, based on Amanda Foreman’s best selling biography, chronicles the life of the extravagant and politically controversial 18th century aristocrat.

Knightley added: "Love scenes are never particularly pleasant, but I thought that they were necessary enough to warrant doing them.

"I use my body as a tool — it’s what I use."