Sigrid, the 21-year-old pop sensation from Norway, looks almost pained when asked to pick her biggest “pinch myself” moment of 2017. In contention, you’d imagine, is her barbed, infectious debut single, Don’t Kill My Vibe, dropping from nowhere and racking up more than 30m plays on Spotify and YouTube combined. She performed at Glastonbury, and a BBC blog speculated that she would return to Worthy Farm one day as a headliner. And talk about range: she also sang at the Nobel peace prize concert, in front of representatives from the 2017 laureate, the International Campaign to Abolish Nuclear Weapons, and an 85-year-old survivor of Hiroshima. “So, so much bigger than a career thing,” she says.

But the single moment Sigrid picks is her set at the Roskilde festival in Denmark back in June. “We were playing at 1pm, which is not the greatest slot,” she recalls. “And it was the end of the week so I was like, ‘People are going to be shitfaced, hungover. No one’s going to come.’ I told the band: ‘We’re just going to do our job, it’s cool to be here, guys, we actually made it to Roskilde.’

“Then we walk on stage,” she goes on, her jaw theatrically dropping, “and there’s, I don’t know, 7,000 people. It’s like: ‘What. Is. This?’ You read stuff like that online and in interviews, but it’s something different when you see the numbers in person. When you see those people actually gone out of their tents, they are probably puking or whatever and they’re like: ‘No, we’re going to go to the show.’ That means the world.”

If 2017 was the breakthrough year for Sigrid, 2018 isn’t shaping up too badly either. On Friday, on the back of just a four-track EP, she was announced by Clara Amfo on Radio 1 as the winner of this year’s BBC Sound Of… poll. The award doesn’t come with a glittery trophy or a generous financial patronage, but it does impart a warm buzz that 170 music experts – from critics to former nominees such as Stormzy and Ellie Goulding – believe you are on a fast track to future world domination. And the Sound Of… list has a decent hit rate: from 50 Cent winning the inaugural competition in 2003 to Adele in 2008 and Sam Smith in 2014.

“Even in high school, music was just a really fun thing on the side,” says Sigrid (full name: Sigrid Solbakk Raabe). “I don’t think I grasped the fact that it could be a profession. And that’s why it means so much to win the BBC prize, because it’s quite unbelievable as a Norwegian. I don’t think there has been a lot of non-American or non-British artists before.”

She giggles, winningly. “To be honest, it’s just a great way to start the year!”

We meet a couple of days before the official announcement. Someone – perhaps from the BBC – has asked for unusual levels of security and anonymity, perhaps mindful of Channel 4’s Prue Leith-Bake Off scenario, when news of the winner slipped out ahead of time. As a result, we sit in a windowless room at the Observer with all the charm of an interrogation cell. Sigrid arrives with a bottle of water and an orange. “Is it OK if I eat here?” she asks, with impeccable manners. And then, as she peels it: “Do you want some?”

As it happens, Sigrid does not draw a lot of attention to herself. Today she wears a very millennial outfit of slouchy grey hoodie with silver trousers and white Nikes. Somewhere between athleisure and sports luxe. There’s no trace of any makeup on her almost translucent, flawless skin; her hair is pine-forest straight and centre-parted.

When I ask how she would describe her look, she says: “Practical, I suppose. When I wake up in the morning, the one thing I think about is being comfortable and wearing enough clothes. Like, today I’m wearing wool, I always have wool on me, because I don’t want to get sick. Because if I catch a cold or get a throat infection, I can’t sing then! And I’ve got to do my job. My style is quite Norwegian, I guess.”

As well as being the politest person I’ve ever interviewed (“Are you sure you don’t want some orange?”) there is an unmistakable steeliness to Sigrid. She says there’s a Norwegian word for it, veslevoksen, which means a child acting older than they are. Don’t Kill My Vibe was inspired by a writing session early in her career with two much more experienced songwriters who she felt were patronising her. And this has led to her having uncompromising views on how she is represented and portrayed in her career.

“Sometimes it’s really weird being an artist, and I deal with that best by being myself,” she says. “And if I can see myself in everything we do: if I can recognise my face, I recognise the outfits, I recognise the artwork, the songs… I don’t like to do a lot with my voice in recordings and stuff, keep it as pure as possible. Keep it raw, keep it honest. I don’t see a reason for why not. Why should I give control away to someone else?”

Sigrid is sometimes asked if success is going to change her. “Why should that happen?” she says, genuinely baffled. “Like they’ll ask: ‘How do you not turn into a diva?’ Well, you’re yourself and I’m so lucky. So lucky to be doing this. That’s the thing: pop music has sometimes had a bad reputation for being about a lot of other stuff than the music. And I am just a lover of pop music. I love pop. I love big choruses. Dramatic choruses: they’re the best thing in the world. And I do this because I love making music and performing the songs.”

The emergence of Sigrid, like Lorde before her, is proof that the music industry still has a knack for tracking down talent wherever it’s hiding. Sigrid was born and raised in Ålesund, the 17th most populated city or town in Norway; a place arguably best known in the UK, until now, for the football club where John Arne Riise started out. Her father is an engineer, her mother an architect, and neither was especially musical. Moreover, Sigrid didn’t even stand out within her own family: her older brother Tellef was a more skilled musician, she insists, and her sister Johanne a better singer.

Sigrid sketches a picture of an idyllic childhood: skiing and hiking in the mountains that surround Ålesund, dancing after school. Piano lessons and singing were just some other things she did for fun. Her vocals had a distinctive natural rasp, but a voice coach encouraged her to embrace it rather than soften it. “I always loved school,” she says at one point. And later: “I have wonderful parents. It sounds cheesy, but honestly, I had a really nice upbringing.” Sigrid imagined she would be a teacher or journalist or work for the government.

From her older siblings, though, she was introduced to the music they were listening to. Sigrid clearly remembers standing on a train platform in France and her brother playing her Coldplay’s Clocks. Another revelatory moment was hearing Rolling in the Deep by Adele when she was about 16. “That was the first time I heard a pop chorus that blew my mind,” she says. “Often you find songs where it’s like: ‘Oh, that’s a nice hook at 3.21,’ but that’s so good from start to end.”

Typically, Sigrid didn’t know what the songs were about. “I had no idea what Coldplay were singing about until two years ago,” she laughs. “I never listened to the lyrics, I only paid attention to the melody.”

This inattention showed when Sigrid began to make music of her own. The first song she wrote and sang, Sun, which was picked up by Norwegian radio, featured the chorus: “Is the weather nice, babe, in your soul?/I think I need some of that sun to shine on me.” “It’s horrible,” she says. “Very cringeworthy, awkward. But I thought all good pop songs needed to be grand and have a lot of powerful imagery. I figured out later on that it was just better to say whatever comes out of my mouth. Just the way I talk.”

Don’t Kill My Vibe was a perfect example of this. Although the lyrics – “You shut me down, you like the control/You speak to me like I’m a child” – could apply to a boyfriend, girlfriend, parent or work colleague, they drip with the disdain and fury of a young person who feels they are being underestimated. Sigrid says that she gets all sorts at her gigs, but the majority are “mostly my age”. A couple of her most devoted fans have had “DKMV” tattooed on the inside their bottom lips.

“I’m scared of getting a tattoo myself,” she winces, “so I was like ‘Whoa!’ That must hurt.”

Sigrid insists that her concerns are the same as those of many 21-year-old women in an age of Trump, Brexit, sexual harassment and climate change. “When it comes to my age, why shouldn’t I have opinions?” she asks. “I think young people have opinions. They always have, but because of social media, you see it much more now I guess. Because it’s so easy just to go out and tweet something or Instagram it, and I think it’s good.

“For instance, everything happening with #MeToo and the feminist movement is going fast and it’s high time it should. The things we are talking or they are talking about, it’s all obvious, it should have happened a long time ago: equal pay, it’s a no-brainer. Still that fight has to be taken but it’s happening and it’s great.” Sigrid will keep being inspired by these subjects: “I think I’ve written one song that isn’t about me. I just find it easier that way.”

Already, 2018 is filling up. She is playing some UK dates in March, then Coachella in the States in April, and that’s followed by a debut album in the summer. But she doesn’t want to talk too much about that yet. “I’d like to be a bit mysterious,” sighs Sigrid. “I’m not a very mysterious person.”

Work continues on that, but there’s a hitch: Sigrid likes to write “angry pop songs”, but these days she doesn’t have much to be worked up about. “Hmmm, it’s easier to get into the emotional stuff when you’re a bit sad yeah,” she says. “But you can always channel your inner emo. Light some candles, turn down the lights, shed a tear. But yeah, I’m very happy now, so I’m wondering what I should write about. Because when stuff happens like the BBC thing: ‘Oh shit, nothing very sad to write about.’”

There’s a little twinkle, “But yeah, I’ll find something.”

Sigrid tours the UK in the spring, starting in Brighton on 12 March, ending in Manchester 24 March. Her single ‘Strangers’ is out now on Island Records