"I want to forget about hair and makeup," she said in an interview with The Times. "Sometimes on a publicity tour I can't remember what time it is, what country I'm in.

"Now it's coming to an end I'm trying to hold on to it. So I have a book, and everyone I've met has a page. I want to remember them and not just be left with the media version of what happened to me."

"We did it two weeks ago," she said. "Four takes one way and two takes with the camera in the other direction. Six takes altogether."

In the interview Watson also picked out Helena Bonham Carter, who played Bellatrix in Harry Potter, as the biggest influence on her career. The pair struck up a friendship after Bonham Carter invited the teenager to her house to discuss their scenes.

"I admire her so much, she is so confident in herself, so happy," she said. "She probably has no idea how important those two or three hours with her were to me."

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.

She has already been offered lots of roles, but mostly of the trashy Shopaholic-genre. “It is stuff that doesn’t make you think. The scripts all have happy endings, they’re really badly written, and they’re sending them to an English Literature student,” she sniffs.

It’s been like that ever since. “Sometimes on a publicity tour I can’t remember what time it is, what country I’m in.” She is so deeply immersed in the final Potter double bill, that she can barely recall filming Half-Blood Prince last year. “I was muddled up. But thankfully I’ve read all the books about seven times, so I remember eventually.”

“The last couple of days we’ve been running for our lives, chased by Snatchers again and again, through the forest,” says Watson. One of the Snatchers, a grey-skinned werewolf, is lining up for pasta Bolognese at the canteen trailer. “They’re real men, which is easier than doing it with an imaginary creature in front of the green screen, but I’m so used to the green screen I don’t mind. I suppose it’s a useful skill.”

But Watson’s two major mentors have been Emma Thompson and Helena Bonham Carter.Recently, Watson went round to Bonham Carter’s house to talk through a scene where her character, Bellatrix, becomes Hermione after taking polyjuice. Bonham Carter wanted to know everything about Hermione, to get the role right, and as Watson admits, “I am a Harry Potter lexicon.” She also found Bonham Carter’s advice incredibly useful. Both actresses started young and are not traditionally trained. “I don’t come, like Dan [Radcliffe], from a very actorly family, so I was Bambi in the headlights – I never had anyone to guide me,” explains Watson. “I hadn’t been to Lamda or Rada, and I had a chip on my shoulder about it. But Helena said I don’t need to get trained: she taught herself, read Chekhov, books, theories, and she prepares herself so deeply for every role – the more you know about a person, the more you move intuitively.”