‘The way it was done was very romantic,’ she says of that kiss. ‘Daniel [Radcliffe] and I have always been good friends, which I think worked in our favour. It’s the only love scene I’ve filmed, but I imagine if you had to do one with some random person that you had no relationship with, it would feel very strange.

'It makes the on-screen relationship make more sense – this idea that we’ve known each other, and in a sense grown up together, off-screen as well as on. Dan is so energetic and really good fun, and the way he works is extremely professional.’

‘My character initiates the kiss,’ she says, ‘which is great because it gives this power to girls and shows that it’s OK to be the one who makes the approach.’

But in real life, Bonnie insists that – despite setting tongues wagging when she stepped out with Twilight star Jamie Campbell Bower at the Saatchi Gallery recently – she is single and making no such approaches, to Bower (with whom she’s ‘just friends’) or anyone else. She has previously joked that she’s ‘married’ to Harry Potter, and, given that J K Rowling wrote the later books after the first few had already been filmed, she’s no doubt flattered that the part of Ginny has evolved so nicely.

‘Well, it’s hard to know if what she’s seen on the screen has influenced the storyline,’ she says modestly, ‘but I’m thrilled that I’ve been given the chance to sink my teeth in and show what I can do. I felt, in the last one, as though I really got to create something worthwhile.’ And so did the critics, who lauded her breakout performance.

But as Bonnie’s presence in the series has grown, so too has the public interest in her. Coping with fame has been ‘strange’, she admits. ‘You can be on holiday abroad, in a tiny village in the middle of nowhere, and someone will recognise you, and you just think, “How far has this spread?”’ Because fame came to her so young, she’s been a bit oblivious to it, she says. ‘Then, all of a sudden, it became a bit daunting. I’ll be out shopping, and all it takes is for one person to recognise me and it can get scary.’

‘He’d read the first two books and said, “You really remind me of Ginny.” I was only nine at the time and didn’t know who any of the characters were, but I read the first one and was hooked. When my mum came home from work, I said, “Please, please can you get me an audition for Harry Potter?”’ So Sheila tracked down the PR for the publisher, who liked Bonnie’s look, and that was that.

‘To begin with,’ she says, ‘we weren’t even acting – we were just being ourselves. Most of us hadn’t acted before; we were hired because we had the right image. We’ve grown up together and we are like a big family. Everyone is lovely, and I think we’re all very inquisitive. When we come back to set after a break in filming, it is like coming back to school.’

The Deathly Hallows, which will be released in two parts (in November 2010 and July 2011), and in which Ginny and Harry get married and have a family. ‘When I read the book, I was shocked that my character had turned into something so big,’ she says.

Bonnie admits to feeling wistful as the end draws near (they wrap next June). ‘We’ve been so busy filming it that there hasn’t really been time to think about the fact that this is the last one. It will be very strange when it’s over and very sad. I don’t think any of us thought about it until the recent press promotion, when people started saying, “The end is near.” And we were, like, “It is?” When we’re filming you forget about the millions of people waiting for it to come out. And then when you turn up at a premiere and see thousands of people, you go, “Whoa!”’

‘I know what Ginny would do in every situation, and relate to her because we’ve both got older brothers,’ she says. ‘But I think all of us who’ve been there from the beginning have got to the point where we want to do something different, be someone different.

‘People always ask, “Is this going to be the biggest thing in your career?” And while I don’t think there’s ever been anything like Harry Potter, that’s gone on for so long and maintained its popularity, I think the answer – for me and for all of us – is that more challenging experiences lie ahead.’