A YOUNG woman is sitting in a suite in a hotel. It is a Monday morning, late June, Edinburgh dripping and mist-smudged. "I'm Eleanor Worthington-Cox," she says by way of introduction. "I turned 18 on Friday. My star sign is Cancer-slash-Gemini, because ..." She laughs. "...I have actually no clue."

She speaks softly, Scousely, although, in truth, she's really from Formby on the coast, so Liverpudlians, she admits, would call her a "wool".

"My favourite snack is frozen peas," she continues. "I don't know why, but they're really good. Get yourself a little ramekin of frozen peas and you're happy."

Say hello to Eleanor Worthington-Cox, teenager, frozen pea lover and actor. Acting veteran in fact. She may have only just turned 18 but she's already been acting for half of her life; on stage and on screens big and small.

You've probably already seen her. Maybe in a Hollywood blockbuster - Maleficent perhaps, where she got to share the credit list (if not any scenes) with Angelina Jolie. Maybe singing her heart out on stage in Matilda (her breakthrough role), or maybe screaming her heart out in Jez Butterworth's Romans-and-Celts stoner drama Britannia (a second series coming soon).

And if not? Well, no matter. You will have every chance in the near future. As well as Britannia, there's a new film, Gwen, out next week, in which she is front and centre in the title role. It's why she is in Edinburgh. The film had its UK premiere the night before.

Watching it, you can tell why she's been working continuously since she was a kid in theatre, TV (she appeared in both Hetty Feather and Russell T Davies's Cucumber, as well as The Enfield Haunting) and film (she turns up in Johnny Knoxville's film Action Point).

"I often joked that despite being a teenager she actually has more experience than I do," Gwen's director William McGregor tells me later.

And yet in Gwen, Worthington-Cox plays younger than her years. A 14-year-old (or thereabouts) with the weight of the world on her narrow shoulders.

Gwen is a proper Gothic melodrama. Set on a struggling Welsh farm it's a rural costume drama that's more prole than posh. You can see the dirt under its fingernails, feel the hunger gnawing in its belly.

Filmed in Snowdonia, it is a cold, bleak, wintry film, sound-tracked by the suck and squelch of mud and perfumed with misery and darkness.

Not a happy film, in other words.

Worthington-Cox is very good in it, by the way. She more than holds her own against the likes of Maxine Peake who plays her sick mother.

"We knew the film would be a success or not based on the casting of the central character," McGregor suggests. "So, we were incredibly excited to meet Eleanor. She has an ethereal quality, but also feels so grounded. She's a genuine shining light at the centre of the film. We go to some quite dark places and she had the skills to make those moments work."

In person it's the grounded quality, you notice about Worthington-Cox. She is self-confident and chatty, but clearly serious about the job.

Gwen, which was shot at the end of 2017, is, she reckons, a kind of horror movie. "It is very bleak, and it is very dark. And that was one of the things that drew me to it in the first place. I love stories where it focuses on the horror within reality. There's no 360-degree spinning heads or demonic dolls. It was all just the horror of the everyday."

It also looked bloody cold, Eleanor. "Honestly, I've never felt anything like it. I remember there was a scene we did where I was sat on a horse about two in the morning - I don't think it's made it into the film - but I'm sat there with the wind just pelting into my face and I went: 'Guys, do you know how cold it is?' And they went: 'It's minus 17, wind chill.' I was like: 'OK, let's get on with it.'

"We had locations that flooded twice and we had actual blizzards happening outside the window."

And, yes, she says, they went out and shot in them. Of course, they did, because it was too good a chance to miss. "You're trudging through mud, you're trudging up and down hills all the time. It takes so much energy from you.

"And I was also looking after a little six-year-old on set, Jodie, who played my little sister. She was so well-behaved. We were cracking jokes between takes. She was doing the splits and trying to teach me. We were having a lot of fun.

"So, the deeply demanding physicality of it all just kind of went over my head until the end of the day, when you'd crash face first on the bed."

When she's not standing around in period costumes in blizzards, Worthington-Cox still lives at home in Formby with her mum, one of her two brothers (the other one has just moved out) and her nan and granddad. Her mum is a lawyer. So not a stage mum, then?

"Not at all. I've always laughed with my mum about the fact that she is the least stagy parent I could possibly have wished for. She's all quite green to this whole thing and it's only been in more recent years that she's been able to spend more time with me and really understand what I'm doing."

Worthington-Cox's career in acting began before she had even reached double figures. "I've always know that performing was the only thing I wanted to do." She was, she admits, the kind of kid who went to see the Royal Shakespeare Company rather than the local panto every Christmas. Her favourite movie as a kid was To Kill a Mockingbird. Later, she got to play Scout on stage herself.

"I've been unbelievably lucky. I started out through possibly the happiest accident that could ever have happened.

“I went to go and see Matilda the musical in Stratford when I was nine years old, just, and I remember sitting there thinking: 'I had no idea that children could do this professionally.'

"I went: 'Mum, I could do that.' And she went: 'Sure thing kid. I think you have to be, I don't know, Angelina Jolie's children to do that kind of thing.'

"And then we saw it was going to the West End and my brother said: 'Oh come on, let's put her up for it. They're doing an open audition. Why not?'

"And 11 auditions later I ended up in the role of a lifetime."

Her very next job was on the Angelina Jolie movie. "They had built a hill entirely for the purpose of me rolling down it. They had this blue screen and they said: 'Pretend there's a castle over there.' And to me it was one of the best things anyone had ever asked me to do. With theatre, it's all very literal. There are props. 'Move to this mark.'

"But for somebody to sit me down on top of a hill and say; 'Pretend there's a castle over there, pretend you're a princess. Roll in these flowers and leaves. I thought it was all my birthdays in one."

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Worthington-Cox is, as you may have already gathered, very much a glass-half-full type personality. What was it like working with Maxine, I ask at one point. "Oh my goodness, what a woman. I couldn't have asked to have worked with anybody better."

When working with actors like her, do you ask for advice? "I feel like it's hardly necessary to ask for it when you can stand in awe watching this person work on a day-to-day basis. We were stood in freezing temperatures in just these layers of skirts and you think: 'That is the kind of woman I want to be; somebody who can be so unbelievably gracious and kind and lovely with all the crew. And hard-working."

And perhaps like Peake, there is a quiet but determined politics underpinning Worthington-Cox's approach. One of the appeals of making Gwen, she says, is that it's a feminist story at heart.

It's also a film that interrogates the belief that poverty is a form of infection.

"Yeah, we've definitely got an anti-capitalist undertone. From my point of view, it's a young woman trying to fight against the patriarchy to build a life for herself and actually support a family.

"The film is set in the 1800s and that I'm a young woman now, saying I can relate to some of the issues, that's quite worrying."

Would she have been able to cope in the 19th-century world of the film? "People my age are so privileged. We've got social media. We've got access to all kinds of things and this young woman is completely isolated.

"You'd like to think you have the strength in you to support a family at the age of 14. But it's so hard to compare. They're two different worlds."

In the second series of Britannia she goes even further back in time. "I don't want to give too much away but I'd say: 'Buckle up because it's going to get pretty rowdy for season two.' This is the punk rock of TV. I think by the time everybody sees series two they're going to think: 'What the hell have we just seen?'”

Beyond that she's got a hush-hush project in 2020 that is going to take all year. She won't be drawn on what it is, but clearly something big then. So, I say, is this what you are going to do from now on? "If I'm lucky enough. This is honestly the one thing I've fallen in love with. It is something that I am completely passionate about. I get up in the morning and it feels like Christmas morning. This is the only thing I want to do."

And when she is not working? "I'm a bit of a home bird," she says.

What's the first thing you do, Eleanor, when you go back to Formby then? "I guess it would be to put the kettle on and cuddle my dog for an hour. She's a minature Maltese. I wanted a tiny, snuggly thing I can smuggle into hotels and bring onto set. Everybody loves Winnie. No work gets done when Winnie comes on set."

For a moment you can see the girl behind the young woman.

Gwen opens in cinemas on Friday. The second series of Britannia will air later in the year.