Photographer Jeff Kaine, who worked with her on topless and other racy shoots over two years at the same time as she did the sex book, said: 'She used to tell us about how much she had enjoyed doing the sex book.
Mills met McCartney at a Pride of Britain charity event and they were married on 11 June 2002.
Some of them see Mills bared her flesh with just her hand, a bag and some clever lighting protecting her modesty.
Now, rare pictures of Britain's most famous models from the time - which range from sexy semi-nude and lingerie shots to playful portraits - are going under the hammer.