In a sun-dappled forest at an undisclosed location in the south of England, three empty directors’ chairs sit under a canopy. The black canvas backs each bear a name in gold copperplate: Daniel Radcliffe, Rupert Grint and Emma Watson. The chairs have done good service, lasting nearly a decade on various Harry Potter sets. When Emma Watson first became Hermione in that chair, she was 10 years old. Now she is 19, a very different creature.

We meet in Watson’s trailer at the end of a metamorphosis that has taken her from a frizzy-haired swot to a sleek, fawnlike starlet now appearing in adverts in Vogue for Burberry and in the front row at Chanel catwalk shows. Potter-geeks might suspect she had recently taken a large dose of polyjuice potion, which famously turns you into someone entirely different.

Inside, however, I reckon little has changed since a small, determined nine-year-old went to audition. “You wouldn’t believe how much I was compelled to play Hermione. I knew I was right to play her, even when my parents were trying to convince me not to. I made it my life for three or four months, just getting through those auditions.” Now Watson is equally determined to bury acting for three years. With four As at A level, having studied obsessively between takes, she is taking up a place in September to study English and art at a university in yet another undisclosed location. She wants to be a civilian again, “like Jodie Foster when she went to Yale,” says Watson. “And I want to forget about hair and make-up.”

On the Potter set, “it takes an hour to get ready every day. They call us at 7.30am.” Watson leans forward across the trailer’s Formica table to show me the extensions plaited into her backcombed light brown hair to give it Hermione Granger’s messy curls. Plus there are fake scars – “They must have rubbed off – I just took a nap” – and plenty of slap to make her lightly freckled skin matt and witchy. The heavy eyebrows are for real, though.

Watson is still thankful she was not forced to wear the buck teeth allotted to Hermione in the books. When she put them in, she couldn’t talk, and the director dumped them, along with Radcliffe’s green contact lenses, both too hard on the young stars. Watson still found her role a burden as well as a pleasure. “When I was little, I didn’t understand that other kids thought I actually was Hermione, really geeky. It was devastating. I thought no one would ever fancy me. And the costumes…”

There was the school uniform, all stiff and buttoned up for Hermione and hanging out for the boys. When the mini-witch was having fun, she wore frumpy, Brillo-pad jumpers in ugly colours. Indeed the Potter series has been a triumph for bad knitwear. “When I was just becoming a teenager, I took some coaxing to get into those horrible jumpers, but now I really use the discomfort, the itchiness, the backcombed hair, to get into character.” She is wearing a fine, thin, Lacoste V-neck in pale beige today, in silent revenge.

Just as Daniel Radcliffe, who plays Harry, had to appear naked in the West End and New York in Equus to dispel the Potter spell, so Watson has taken up the offer to be the face of Burberry next autumn. She wears those raincoats well on her tiny frame and looks more vampish than ever before. “I didn’t actively calculate all this…” Watson shuts her eyes and frowns. It’s a very Hermione moment. “I guess it’s helpful for me to be seen away from all this. You know: she can look different, she is older, she could be cast in other roles.”

With the help of a sensible publicity machine, Watson is carefully navigating the whole transformation into siren – choosing Burberry which is sharp and chic without even a hint of trashiness. Clearly glamour is a relief after playing the ultimate swot.

Growing up on set

In other ways, the charming, polite Watson seems less sophisticated than many 19-year-olds. There is a lack of knowingness about her, no fakery or front. Of course, cosseted on the closed film set, she has been largely denied the normal opportunities for teenage sin and stupidity, despite going back for part of every year to be with her friends at Headington School in Oxford. “I don’t feel I’ve missed out. Sometimes people text me what they’re doing and I think, I’m glad I’m not there. I don’t have to do that. And I’ve gained so much here.”

Today she is promoting Harry Potter and the Half-Blood Prince (out in July) while wrapping up filming on Harry Potter and the Deathly Hallows I and starting work on Deathly Hallows II, the final film. Yes folks, that’s eight Potter films, on which Watson and her colleagues have pulled 12-hour days, for most of each year. During her A levels, a tutor worked with her on set for three hours a day, and Watson revised in any spare moment, even while she was getting her hair done. “God knows how many hours – years – I’ve spent on set, but my driver Nigel was trying to work out how many hours he’d driven in the car, and says the distance was twice around the world on the last film. And then he’s got to get himself home.”

There is a comfortable, family atmosphere on the set, and Warner Bros have attempted to keep the same crew throughout the series.

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