Katie Leung is 23 years old, one of the stars of the most successful series of British movies in the history of British movies, the first girl to kiss Harry Potter and, as such, part of pop culture history.

She is also a photography student. It’s being a student that she cares about most these days.

On the first good day of the year we are sitting in a tiny cafe in Edinburgh’s Grassmarket, not far from the Edinburgh College of Art, and Leung is showing me photographs of empty carparks. Grids, lines and warning signs. She quickly flicks between them on her iPhone. “There’s not much difference, but there is,” she points out. She’s very pleased with them. “The most boring thing I’ve ever photographed.” But that’s what’s great about them, she says, “because I didn’t have any emotional attachment to these pictures. And they turned out really well.”

In person, it should be said, she makes more sense as a student than as a film star. Leung couldn’t be any less film-starry if she tried. She’s chatty, slightly scatty, and I’m guessing the comfy cardy she’s wearing was probably not made by Burberry. I offer her a coffee but she says she’ll stick to her half-empty bottle of Lucozade.

Maybe it’s because her film-star moment is already behind her. She finished filming her role as Cho Chang in the last Potter movie “quite a while ago”. And though she still has an agent in London she’s not sure when – or if – she’ll return to acting. “I definitely haven’t thrown it out the window, but I’m thinking I should graduate before I think about anything like that. I definitely don’t want to give up my uni for acting at the moment.”

For the time being she is happier behind the camera than in front of it. In a way maybe she always was. “I’m quite a timid person,” she tells me at one point, “an introvert if you like. And I think that shows in a lot of my images.”

She shows me some more photographs. Images of her granny’s vacant flat, images that try to capture the wind. “I like to take things in the moment as opposed to composing something, setting up an image. I haven’t learned to work with lighting as such, so a lot of my work is based outside using natural light. And it’s candid as well. I try to be very secretive.” You’re nosy, Katie, is that what you’re saying? “I am. I’m very nosy. But I pretend I’m not.”

She’s not totally foresworn her celebrity cachet. She’ll use it when it’s useful. The reason for meeting today is her involvement with the charity SCIAF’s Wee Box Big Change campaign. “It’s basically giving up a luxury for Lent. You put the change that you would normally spend in this little box and then you donate this money to charity. I chose this one in particular because it’s based in Glasgow, and I think it’s really important when you have an involvement in the charity that you do a little task as opposed to just giving money. And it stops you from eating tons of crisps and sweets.”

That’s what you’ve given up? I thought it was chocolate. “Yes, it’s chocolate. I guess chocolate because I’m not a huge fan of chocolate anyway.” She’s feeling the benefit, she says. “I’m not religious in any way, but it’s good for the stomach.”

Leung was born in Motherwell, where she still lives. If you could take a photograph to represent your childhood, I ask her, what image would you take? “Just a field,” she says quickly. “A huge field with nothing in it. Just a space.” And that represents what? Freedom? “Yeah, it does. The world’s your oyster.” Childhood was playing in the streets, she says, having no responsibilities, “and getting the benefit of the doubt, getting away with things”.

Leung didn’t spend much time with her parents growing up. She was just three when they split. She stayed with her dad, Peter, but he was working all the time: “My gran brought me up.” There doesn’t appear to be any great trauma here. Her parents remain on good terms and she’s now got stepbrothers and stepsisters, “so I wouldn’t change it for anything”.

Even so, it may or may not be significant that when I ask her for one memory of her Harry Potter experience, the day she offers is her audition. It was her dad that spotted the advert for the casting call. “It was a really nice moment because my parents hadn’t seen each other for a long, long time and both of them accompanied me to the first audition. It was just a really nice feeling to stand in the queue for however many hours and, at that point, it wasn’t about getting the part.”

She did, of course. She was 17 at the time. “Looking back, when the film started and doing my first interviews I was so naive and really just so innocent. I didn’t know much about anything, really. I’d always been sheltered by my parents. I feel I’ve moved on a lot from there. I do feel very grateful for it all and people remind me I was very lucky to be part of it.”

It was while travelling to promote the films that she decided she wanted to take photographs. She’d go to visit family in Hong Kong and try to capture the rush and jostle of the place. “I love it that everyone is so aggressive. There’s no manners as such because they’re so hard-working.”

She’d take pictures of people, strangers on the street. “It’s just that adrenalin rush you get when you get caught taking a photo. I tend to take pictures of the elderly. I don’t know if it’s because if they do see me I can run away. But at the same time, I think it’s about being aware of ageing.” Katie, you’re 23, I point out. “Death is quite a big deal to me. That subject is on my mind ...”

Five years from now, she says, she’d like to be “abroad, photographing images that people are going to look at and think ‘wow, I want to be there, too’.”

Given all her international influences, how Scottish does she feel, I wonder? “I feel very Scottish. I don’t go out drinking as much as half my friends do. I like to stay in and watch a good movie, but in my earlier years I did go out a lot and went clubbing and all the rest. Jaegerbombs. That’s Scotland to me. I don’t join in with those games any more.”

She’s looking forward to the premiere of the final Harry Potter movie this summer. “That’ll be a lot of fun. You go through so many months of filming and it’s just work, and it’s not until you attend this one event that suddenly you realise how massive it is.”

But in the end everything comes back to photography for her these days. “Now that I’ve studied photography I’m even more image-conscious. Not in the sense that I want to look pretty in front of the camera or I want to doll up. It’s just that I hate normal pictures. I hate it when people smile for the camera. I prefer something quirky and original.”

Like empty carparks for example. “I didn’t have permission to photograph in this business park near my home in Motherwell,” she says as she shows me the pictures again. “My friend introduced me because he used to meet up with his friends there and they would show off their cars.” He was a boy racer? “Yeah. Thankfully not any more. I actually almost got arrested. On my last shoot I got asked to move and I was at the stage where I’d put so much work into it that I wasn’t leaving without this last image. They took down my registration details and all the rest. I’m glad I stayed.” No letters in the post afterwards? “No, no.”

Katie Leung isn’t a kid any more. But she’s still getting the benefit of the doubt.

The Scottish Catholic International Aid Fund’s Wee Box Big Change campaign continues until April 21; for more details visit www.theweebox.org. Harry Potter And The Deathly Hallows Part I is out on DVD on April 11; Part II is in cinemas on July 15