I spot Cara Delevingne outside the swanky London hotel where our interview is about to begin. But the first thing I notice is a group of ecstatic teenage girls fanning over their idol. One of them (she looks about 10 or 12) asks the supermodel to add her on Instagram. "Not a problem!" says Delevingne as she takes her phone out and grants the girl's wish. The lucky fan starts shaking so hard she can't even say thank you. Delevingne looks back awkwardly at her publicist, not knowing what to do.

But when it's time for our interview, she's clearly in control. She climbs onto the chair with her feet and is willing to answer any question at all. She's young, feisty and a bit crazy, just like her heroine Margo from Paper Towns, which just opened in cinemas worldwide. They're both a good kind of crazy though, which I'm quick to tell her. "We're both fearless," Delevingne corrects me. "That is for sure the personality trait we share."

Cara Delevingne on being rejected and how she struggles to stay skinny

Have you always been like that or is that a result of your career?
I've always been a thrill seeker. People say I'm very spontaneous, I think I'm very predictable. I just always go for the most exciting things I could find in life.

Margo pulls a few outrageous pranks in the movie. Is that something you're capable of too?
I used to run around school and we used to have these giant sugar pots on the tables and I would go and replace the sugar with the salt and the salt with the sugar. Still have no idea how I never got caught. I would cause the trouble but never got in trouble myself.

Shall we name the school so it could finally become public knowledge?
Let's say I went to Hogwarts. Oh my God I just remembered I used to buy henna pens and draw penises on people's faces when there were sleeping! Although people quickly figured out who was responsible - the only girl with no penis on her forehead in the morning.

So you and Margo have a lot in common, but how do you differ?
She does pranks as revenge. I do them to people I love [grins].

Cara Delevingne on being rejected and how she struggles to stay skinny

You must have been always surrounded by people trying to befriend you. What was high school like for you - did it verge on Mean Girls?
Nothing like that. I went to Hogwarts, remember? Harry was an arsehole though...

You're a model, designer, musician and actress - any more hidden talents?
There isn't much left in my talent basket... I'm actually a good magician. If all fails I might join the circus. Also I love bread baking.

Do you actually eat bread?
I do but I can gain weight easily. Trust me. It doesn't take a lot.

Do you diet at all?
Of course I do. For Suicide Squad I'm meant to be a goddess. 'Ripped' as they say. So I've been doing a lot of training. I have to eat a lot of protein and vegetables. No carbs.

How does it feel to be on that diet?
Very boring. But again I would do anything for a good role, except for probably plucking my eyebrows!

What do you think is more difficult - breaking into modelling or the film industry?
They are both pretty f**king hard to get into. As for modelling: I felt like because I didn't give a sh*t at all, that's why people wanted to hire me. I think it's ridiculous how many people want to be models and are so desperate about it. The fact that they are so eager makes them far less appealing. In modelling I feel like there are so many models - they'll use you once and you can be gorgeous but no one will ever ask you back again. Acting is like - once you're in you're in. You get picked up a lot more, if you're good.

Cara Delevingne on being rejected and how she struggles to stay skinny

You're a Brit It-girl. How easy was it to play an American in Paper Towns?
I love accents so I started my prepping there. In the film I wanted to make it as natural as I could, so I kept my accent when I wasn't on set. Which for my family and friends was very weird. I started dreaming in American. I would wake up and think in an American accent.

At one point in the film Margo says that she might have cultivated her image. Can you relate to that?
I'm not trying to cultivate a fantasy. I specially told my fans, this 'being Cara Delevingne' kind of fantasy is completely false. I'm no better than anyone else, I'm as human as anyone. I kind of try to get rid of it as much as possible. But again I guess I do like to make things look easy - I just think it's part of my job.

What about your wild image? Where has that come from?
I play music, I like leather. There you have it. What else can I say? I'm wild, but more feral than wild. I don't like to be caged.

Have you got a dream role?
I'd love to play in a movie set in the future. Like the first female Formula One champion or the first female US president, which will hopefully happen soon.

Have you auditioned for any great roles you didn't get?
The first one  - it was Tim Burton's Alice in Wonderland. I was 16 and I thought I was made to be Alice. That was my first taste of rejection. It took me so long to get over that. I didn't watch the film because I was so upset I hadn't got a part. When I finally watched it I disliked Mia Wasikowska because I was so upset. I'm a very bad loser. These days when I go for a role I automatically think of three people I know who would be better at it. 

Cara Delevingne on being rejected and how she struggles to stay skinny