Portrait: Anna bares all

Until I was 10 years old, I was the youngest of four, and I know my brother and sisters really adored me. I think I was quite sweet - and quite sweet looking. I didn't have much to moan about. We had good-looking parents, and we were all good-looking in a way.

We lived in the country, and were often quite bored; my sisters, Isabelle and Kate, and I, would often stand staring at ourselves and talking in the mirror. I remember one day standing with Isabelle, looking in the mirror. She used to call me "Posy" and tickle my fat cheeks, and had obviously found me a physical delight, but she said to me, "Anna, what has happened to you? You used to be so sweet." I must have been about 11, and on the turn. That did kind of pierce my heart.

Isabelle was the oldest, so she was the one who first went out into the party scene. Because I was younger, I imitated her and Kate. They'd say, "Anna, try this," or, "Anna, I've got a leopardskin top that would look good on you."

I went to a convent boarding school which was very strict. We had to wear a brown school uniform and two pairs of knickers, a white pair and a brown. In Shaftesbury, in Dorset, we were known as "the welly brigade", because we were allowed to walk into town, about three miles over the hills, but we had to wear Wellington boots. It was the time of punk rock, and I always wish I could have got out of that environment and gone full-on punk.

At 16, I came to live in London. I was meant to go to sixth- form college, but I became an artist's model, I used to sit for lots of painters. I never minded taking my clothes off. Ron Kitaj did a few drawings of me. And a friend of mine, Luciana Martinez, painted several portraits of me stark naked. I got pounds 15 an hour, and I was very good at it, I used to love it.

Next I went to LAMDA drama school in London, and although I wasn't self- conscious in other ways, I was not confident about my talent. The teachers at that particular drama school didn't take to the type of person I was. One teacher said to me, "Look at you, Anna. You're a mess. Your hair's all over your face. You walk in this terrible way." I was a bit gawky and gangly, but that wasn't constructive.

I had to leave LAMDA because I got pregnant, and that was a change of self-image. I couldn't stop eating. I wanted to be like a cow in a field that could munch for 24 hours. I couldn't find clothes to fit, so I had this huge gingham dress, like a tent, made for me. I look at pictures of myself in that gingham dress and ankle socks, and I just look like such a fat teenager.

I don't know if you're always your own best judge of how you look, but I love buying clothes, and I think by now I know what suits me. I don't wear make-up every day, and I wouldn't know how to spend a long time doing it. I'm torn between thinking that it's nice to care about these things, and nice not to care. As an actress I have to dye my hair, because it's quite grey, and to go to the dental hygienist. And maybe all that sort of thing should come naturally. I'm 34, and part of me thinks, "Anna, you ought to make a bit more of an effort, anyway." Self-care does seem to equate to self-respect. But personal grooming very much depends on how you were brought up. We grew up in the countryside, and our nails were always full of horse shit. The idea that you would file them was anathema.

Health, obviously, is important to me. I love walking, and when I take my daughter Poppy to school, I walk for an hour in Hyde Park, but the whole concept of "feeling the burn" makes me want to run. Those hormones you produce, endorphins, I find a depressant. I don't like gyms but I did go to one recently, because I had to appear naked on stage, so I thought I'd better. It was for a part in a play called Spencer, at the National Theatre, about the painter Sir Stanley Spencer. I had to drag Anthony Sher round the stage by my knickers every night.

I've got stretch marks, and I breast-fed for a year, so my body isn't perfect. I didn't take my clothes off on stage thinking, "There you go, guys. Lucky you!" But I feel that, when they sell Nicole Kidman to us as being the epitome of sexiness, that is an attack on real sexiness. To confuse physical perfection with actual female sexiness, or eroticism, or reality, is a terrible mistake. There's nothing I want to change about myself. I do find I'm interested by the process of getting older - just so long as I feel that I am catching up emotionally.

Anna Chancellor appears as Regan in Yukio Ninagawa's production of `King Lear', in Japan from 22 Sept-11 Oct, and at London's Barbican Theatre from 22 Oct-20 Nov