Fantasy girl: British actress Sophie Turner has said that her Game of Thrones character is her "first love".

It feels appropriate that when I meet Sophie Turner, the 19-year-old British actor who plays Sansa Stark in the hugely successful television series Game of Thrones,

a solar eclipse is plunging part of the earth into darkness. It almost sounds like a plot line.

Sadly, neither of us sees anything – where we are in east London, it is cloudy and cold. Turner has arrived bang on time, dressed in high-waisted skinny jeans and a parka, yawning. "Excuse me," she says immediately. "I'm not used to getting up at 9am."

Perhaps not this week but when she is on set, as she has been from July to December for the past five years, she works a 12-hour day.

"I sleep whenever I have a spare moment," she says, laughing. "If I arrive on set and they tell me I have five minutes before hair and make-up, then I head straight to my trailer for a nap."

Filming for the show takes place in Northern Ireland, Malta, Croatia, Iceland and Morocco. "I've mainly been in Ireland lately," Turner says.

"I wish I was back in the sun."

For the uninitiated, Game of Thrones is a mediaeval fantasy epic, adapted from the sprawling novels by George R.R. Martin and featuring a cast of thousands.

It is set largely on the battle-scarred continent of Westeros, where clans scheme and slay each other in attempts to seize the throne and rule the seven kingdoms. At the same time, they face imminent threat of attacks from the queen of the dragons and her army across the sea, the former king's youngest brother, who has a creepy priestess on his side, and an even darker force – the terrifying "Others" – bearing down from the north.

Turner has been playing Sansa Stark, one of the show's leading characters, since she was 14. "I've grown up with her," she says. "I really feel what she feels; I probably know her better than I know myself."

Sansa is the eldest daughter of Eddard "Ned" Stark, Lord of Winterfell, and his wife Lady Catelyn. Lord Stark (played by Sean Bean) was beheaded at the end of season one; Lady Catelyn had her throat slit at a wedding two seasons later.

The threats of violence to Sansa have increased with each series. "Every scene has been a crying scene for me; it's been very emotional," Turner says.

Game of Thrones is notorious for its sexually explicit scenes. How much did the very young actors at the centre of it all understand?

"It was strange to start with," Turner says. "When I first read through the full script, I was with [her on-screen siblings] Maisie [Williams, who plays Arya], who is a year younger than me, and Isaac [Hempstead Wright, who plays Bran], who is three years younger, and we were sitting there, reading, looking up at our parents – like, 'What is this?'"

As child actors, each had a parent on set as a chaperone. Turner's mother gave up her job as a nursery school teacher to accompany her daughter, mainly in the first three years, to Croatia to film.

"I really needed her with me," Turner says. The first time her father came out to the set, as a surprise, Turner was about to film an attempted gang-rape scene.

"It was horribly awkward," she says, cringing. "My dad didn't know this scene was going on, he just thought he'd turn up. We were like, 'Oh, bad day, Dad.'"

Were her parents shocked? "I think in the beginning they were – there were so many sex scenes in the first series – but after that they got used to it. They knew it was a good-quality show."

Amusingly, Turner says, her mother still sat her down aged 16 to talk about sex. "I said, 'This isn't necessary, I know everything. I know every single thing that a person can do – and more.' The show is very inventive."

Sophie Turner started acting aged three, when her mother took her to drama class, "mainly so she could have a cup of coffee for an hour", Turner says. She grew up in a large Edwardian house with two older brothers, whom she adores, near Leamington Spa in Warwickshire, England. "My childhood was pretty fun. We had pigsties, barns and a paddock, and used to muck around in the mud." The pigs and horses have now been joined by Zunni, the dog that played Turner's on-screen pet wolf, which she adopted after the first series.

All through her childhood, Turner knew she wanted to be an actress. She remembers when she was 11 telling someone that she would have to break into acting relatively soon if she was going to make it.

"I've always had my business head on, it's never been just a hobby," she says. She turned down a place at the Royal Ballet School the same year. "I knew it would have to be drama or ballet and I chose drama."

Family is evidently important to her. She describes her brothers James, 27, and Will, 25, as her best friends. "They keep me grounded. I need that," she says.

The Game of Thrones cast and crew are like extended family, too – Kit Harington, who plays her bastard brother, Jon Snow, is a surrogate brother, as are the American directors David Benioff and D.B. Weiss. Maisie Williams, her on-screen sister, is a cross between a best friend and a sister.

But it is Lena Headey, who plays Cersei Lannister, King Joffrey's mother, from whom Turner says she has learnt the most about acting. "She's so fascinating to watch. She can convey so much with just her eyes."

She would like to study at some point – psychology or history – but says, "I just don't know when I will have time."

What other aspects of teenage life does she think she has missed out on? "Maybe relationships," she says. "But I was never that fussed about it. I've always been more dedicated to my work than boys."

The writers of the show are notorious for killing off characters suddenly and violently. Every season they pull a prank on a member of the cast, giving them a fake script involving their death. "Then they leave it for about three weeks before they tell them they're okay," Turner says, shuddering.

The thought of Sansa being killed off fills her with dread – and not just because of the lack of work. For a child actor who has played her for a third of her life, it is more profound. "I would miss Sansa," she says, "I love her. She's half of me and I'm half of her."