The British actress Helen McCrory, 39, who will appear in Harry Potter and the Half Blood Prince as Narcissa Malfoy later this year, features alongside Daniel Craig in the new Baillie Walsh film Flashbacks of a Fool, which opens in cinemas nationwide on Friday. She is married to fellow actor Damian Lewis.

It was interesting to play Cherie Blair in The Queen. She was a character that went from being naturally self-conscious - as everyone is when they're in the public eye - to someone who became very well groomed and, I thought, even more self-conscious.

It must have been very hard to be the Prime Minister's wife. You have never asked to be judged as a beauty or a fashion icon. To be so heavily criticised must have been very hurtful to her.

I met her briefly once, many years before we did the film. She came to the theatre to see a play at the Almeida and I met her afterwards. I liked her - she was very quick to smile and, as you would imagine, intelligent and erudite. She was very witty, actually.

All her suits were copied in the film; the costume designers would look at cuttings. What she wore made an enormous difference. Just as it does to anyone, whether you are putting on high heels and an evening dress, or a pair of old welly boots and dungarees to go to the bathroom. It affects the way you walk, the way you see yourself, and for someone in her position, the way people perceived her.

On Flashbacks of a Fool, I worked with Daniel Craig, not James Bond. He didn't pull a gun out once. He didn't mix a martini either. He certainly did not try to get me into bed. In the film, the young Daniel Craig wears shorts that, quite frankly, are only seen in gay pornography. The girls wore fantastic pink and silver belted dresses with the flicked hair and blue eye shadow. It's a very stylish film because Baillie [Walsh, the director] has such a good eye. He was present at every single costume fitting. I am playing this rather eccentric gardener that I based on Elvis Presley.

Music really influenced me when I was growing up. I did go through a Jimi Hendrix phase. My hair was naturally quite afro, and I wore low-slung jeans with very high heels. Siouxsie and the Banshees had a lot to answer for. I was in a top hat with peacock feathers and thigh-high black boots. I was 17 - old enough to know better.

I play Narcissa Malfoy in the new Harry Potter film. If I told you what I was wearing, I would probably have to kill you; it's a bit like working for MI5. My costume is very couture, with beautifully sculpted silhouettes. The costumes are designed by my Parisian friend. Of course, style was battered into her at an early age.

In Charles II [the BBC series], we had a lot of nude scenes. I didn't want to do them. So instead, Joe Wright [the director] and I looked at the original prints and paintings of the time, and talked to various historians. At the time women didn't wear a lot of corsets. They almost wore bed robes, which are very sensual.

If you're walking around, basically in your nightie and a great big silk dressing gown, and huge wigs with white powdered faces and little cupid lips, it's a very sexy look. Quite artificial really: it reminded me slightly of a geisha, which I know is sexy, but very restrictive. I had the feeling of having a mask on. I like that - the mystery of dressing. I like it when women have an air about them.

I love the fact that I have a pair of hips and a bit of a chest. My shape changed enormously after pregnancy. Now I am learning to dress a different figure. I have no desire to do battle with my weight.

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