Katy B is looking to translate her success at home to success in the States. (Jennifer S. Altman/FTWP)

“But I’ve scrubbed up a lot,” says the 22-year-old British singer over breakfast. “Before this, I would go onstage in my ex-boyfriend’s old jumper ... I wouldn’t wear any makeup. I wanted people to like my music and not care how I looked.”

To American retinas, pop stars are the people who wear frocks made of flank steak and brassieres that shoot Cool Whip. Katy B wears jeans, sneakers and two little black apostrophes dabbed to the corners of her eyes.

But she sounds like a pop star, without question. Her debut album, “On a Mission,” out this week, is a triumphant balancing act of bold rhythms, bubblegum melodies, youthful honesty and old-soul poise — exactly the kind of album that continues to elude so many American superstars.

When Britney Spears sings about dance floors, it’s difficult to imagine she’s ever stepped on one. When Katy B sings about dance floors, you feel them under your feet. Then you feel the butterflies in your gut, the strobes flickering through your eyelids, the bass tickling your nose, the Red Bull splashing on your Reeboks, the ineffable adrenaline of youth. If Taylor Swift grew up in London’s underground club scene, she’d be lucky to have written songs that feel as true as these.

The tiny singer and her tiny entourage finish breakfast and file out of the Midtown cafe and into a big black van. She’ll spend the rest of Tuesday afternoon ping-ponging around Manhattan to promote “On a Mission,” an album that her handlers are hoping to pit against the likes of Britney, Katy Perry, Ke$ha and Lady Gaga. It’s a constellation that the singer has a hard time imagining herself joining.

One of the crowd

“People expect you to be this weird cartoon sometimes, when you’re a musician,” Katy B says. “I hate that. I hate standing out. I hate people looking at me. I just want to be part of the crowd.”

That’s increasingly hard in Britain, where “On a Mission” was released earlier this year to wide acclaim. It was nominated for the annual Mercury Prize — an award that eventually went to PJ Harvey — and Katy spent her summer singing to enthusiastic crowds on the European festival circuit. She’ll return to the United States for a tour early next year.

For now, the goal is to try and become a pop star without actually becoming that kind of pop star.

“I enjoyed being Katy B before this album came out,” she says. “I enjoyed being myself and my friends and my life, and I don’t really want to change it.”

She’s a student of pop music, literally. Before earning a degree in popular music from Goldsmiths College in London, Kathleen Brien graduated from London’s BRIT School, a school for the arts whose alumni include the late Amy Winehouse, Leona Lewis and Katy’s classmates Jessie J and Adele.

London’s nightlife was just as educational. “I went to my first drum ’n’ bass rave when I was 16 and remember being terrified,” Katy says. “Looking around, trying to figure out how to dance to this music, watching some girl in some hot pants, trying little ways to learn her movements.”

By the time she was 18, she was balancing her nights in clubland with her days at Goldsmiths (where she studied alongside current British sensation and fellow Mercury Prize nominee James Blake).

“My first day there, they showed us videos of people, like, hanging themselves from hooks on the ceiling and smearing blood all over their faces,” she says. “And then they said, ‘Go write a song about this.’ ”

Katy B performs at August’s V Music Festival. . (AP Photo/Joel Ryan)

“In the end, she was kind of better than the music,” says Sarah Lockhart, co-director at Rinse, which is now a licensed radio station and a record label. Instead, Katy began working on her own album with producers DJ Zinc, Benga and Rinse founder Geeneus. Her popularity in the underground quickly grew so widespread that it shot her up the British pop charts.

Now Lockhart is traveling with Katy in New York, wondering how they can pull the same trick in the States. But in a foreign land where the singer’s credibility isn’t worth as much, the hooks have to speak for themselves.

“Ultimately, it’s a pop record,” says Lockhart. “But she’ll cringe at that word.”

Let’s try it. Is Katy B a pop singer?

She laughs. “I’d rather just be a singer,” she says. “I’m not trying to take over the world or be a real athlete with it, if you know what I mean. I just enjoy making the music.”

She’s just finished an equally low-key interview with MTV in Washington Square Park, where her biggest confession was that she’d auditioned for the role of Hermione Granger in the “Harry Potter” films as a child.

In the van on the way back to her hotel, she rifles through her purse. It contains a paperback copy of David Nicholls’s “One Day” (which she plans to finish before seeing the movie) and a bag of Sour Patch Kids (which she shares).

Weird to have fans

Ask Katy about what her fans get from her music and, voila, you’ve found the word that makes her cringe — or at least an idea that vexes her. “I find it weird to have fans, actually,” she says.

Five hours later, the Studio at Webster Hall is crammed with a few hundred of them. They press toward the stage as the singer joins her six-piece band for her first U.S. concert. Her singing is both strong and effortless, especially during “Perfect Stranger,” a tune she recorded with dubstep supergroup Magnetic Man about the moment when dance-floor anonymity transforms into communion.

As she works the stage in jeans, T-shirt and hoop earrings, it feels like counter-programming to the splashy absurdity of an American pop concert. This isn’t a pop star singing about me, me, me, nor a Gaga-style affirmation for you, you, you. It’s about the cult of us.

When the digital stutters of “Katy on a Mission” come rippling from the speakers, the room erupts with fresh energy. “My limbs seem to move what the beat dictates to me / I push in to the middle, the sound becomes a part of me,” she sings, imagining the beat and the body as one. When it’s over, the audience roars.

Katy claps, too, as if she’s part of the crowd, not the reason for the applause.