Keira admits 'I love stripping off for photos'

Yet far from shunning the limelight, the 22-year-old is starring in an advertising campaign for fashion house Coco Chanel, in which she appears naked – covering her breasts with a bowler hat.

In an interview in the latest edition of Vogue, Miss Knightley admits she is trying to 'have her cake and eat it' by taking her clothes off for advertisers while at the same time demanding privacy.

The new pictures follow a similarly revealing shoot for the cover of Vanity Fair magazine last year.

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Hats off: Keira's Chanel advert

Miss Knightley, who has in the past been vociferous in her condemnation of photographers pursuing her in public, was challenged during the Vogue interview on the apparent contradiction between her complaints about intrusion and undressing for a billboard poster.

She replied: 'Of course I want to have my cake and eat it. Who doesn't want to have their cake and eat it? Show me that person.'

And the actress defended the advertisement, saying it was 'something to show the grandchildren', adding that posing for the pictures was a way of overcoming her own 'inadequate' feelings about her body.

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Vanity Fair: Keira with Scarlett Johansson and Tom Ford

Miss Knightley has in the past been brutally honest about her body shape, particularly her lack of cleavage. She has now revealed her angst at being criticised for being too thin.

'When I was 17, 18, 19, I felt incredibly insecure,' she told the magazine. 'I went through a period of thinking I looked weird and too skinny, and that's ten times worse when you're being written about.'

She also spoke of how life on a film set – where everything is done for you – can place extra pressures on young actresses, particularly in the glare of publicity.

'When you're told that you have everything you wanted, even when it wasn't what you wanted, and you're not feeling great, then you feel depressed and insecure because you should be grateful,' she said.

And she added she had considered leaving the country to escape the attention and, according to the magazine, even thought about giving up acting. She has no such reservations about her new Chanel adverts, however, describing them as 'fabulous' and 'exciting'.

The campaign, for the Coco Mademoiselle fragrance, also includes a glamorous 60-second cinema commercial, shot by Atonement director Joe Wright, which features Miss Knightley slipping out of the bowler hat outfit into a crimson dress, dashing across Paris and flirting with a mysterious stranger.

The Chanel adverts are the second time she has appeared nude for a photo shoot, after the Vanity Fair cover by renowned photographer Annie Leibovitz, in which she posed alongside American actress Scarlett Johansson and designer Tom Ford.

'It made me giggle,' she said. 'It was one of the best photographers in the world and you're 20 and you go, "Why the hell not?"

'There are huge contradictions in people. And there should be. On the one hand, I was completely self-conscious about my body, on the other I love nude photographs and one way of getting over feeling inadequate is to go, "Sod it, you are getting over this." And just do it.'

Miss Knightley, who was nominated for an Oscar in 2005 for Pride & Prejudice, has been lauded by critics for her performance in new British film Atonement, in which she stars alongside James McAvoy as an uptight society woman of the Thirties.

She admits she was happier making the film than Pirates Of The Caribbean – shot when she was still a teenager.

She explained: 'You're too young to drink in America and you're on your own, and you don't know anyone and you can't drive, so you're sitting in your hotel room and you're just watching television – maybe even a programme about how lucky you are.'