'It's the first time I've been anything but Hermione,' she says, fiddling with the cushions. 'Pauline is headstrong, so in that way she is quite like Hermione, but she is not academic. In fact, she actually reminds me of myself as a child, much more than Hermione does. Pauline is utterly obsessed with being an actress and I was just like that when I was younger. I dreamt of it. I practised speeches in front of mirrors. Whenever there was a part at school, I went for it. I was probably a bit of a show-off in the sense that any chance to get up and be seen, I did it.' She sounds like a nightmare. 'I was such a drama queen,' she says, blushing a bit. 'I used to wail and moan and cry, and little things were blown up into being big things. I don't know how my parents stood it, really.' She says she isn't like that at all now. 'I've grown up a bit,' she says. 'I've had to.'

The upshot, though, is that not only has most of her childhood been documented on film but that she has hardly had one at all. Does she see her childhood as abnormal? Watson thinks a bit. 'Yes, I suppose I do,' she says. 'I am very focused and very motivated, so I have tried very hard to combine being an actress with being a student, and so far it has worked out OK.' I tell her that I wasn't actually referring to her academic life. She is obviously highly intelligent. Not many girls could be filming for nine months of the year and somehow get A grades in all four AS levels as Watson did last summer. She still has two Harry Potter films to shoot - she will be 20 when the final installment is completed - but is applying to Cambridge to read English and philosophy. 'I feel it's terribly important to continue with my education, in case acting doesn't work out for me.'

She's always being asked about her relationship with Radcliffe and Rupert Grint, who plays Ron. 'We're good friends,' she says. In the summer she was rumoured to be dating the young Wasps rugby star Tom Ducker after they were spotted on holiday together on the Riviera - according to press reports they split up last month. Then she hit the front pages of the celebrity mags when she turned up at a ball with her fellow actor Henry Lloyd-Hughes, who had a bit part in the fourth Harry Potter.

'The thought of all this publicity chills me to the bone,' she says. 'I hate seeing my name on the front of a magazine. I'll walk past a Tube station and see something about me, and I try not to read it but it's hard. Who doesn't want to read about themselves? But it's always written with this tone - as if the person knows me. But they don't.' But that's the point, I tell her. We all do feel as if we know her because we can trace her back to being 11 years old when she wore sweet Pauline Fossil-type dresses to Potter premieres. In fact, the more I think about it, the more like Pauline she seems. Both barely have a life, bar acting. But surely there must be upsides to the job. 'Oh, absolutely,' says Watson firmly. 'I've met some amazing actors.'

Does Watson think that it is remotely relevant to girls of her generation?

'Yes, I still think it's relevant,' she says enthusiastically. 'Everyone loves that world, don't they? The backstage world of what actually goes on during the rehearsals of a play or the making of a film. I thought it would be so glamorous, so exciting.' And isn't it? Emma Watson looks at me in surprise. 'Yes,' she says, eyes open wide, 'of course.'