Picture the scene: A dinner party. It could be any dinner party, anywhere in North America or Europe, taking place at any point in the last 30 years, but this one happens to be a fictional dinner party thrown by Nathan (James Tupper) and Bonnie Carlson (Zoë Kravitz) in Big Little Lies, the hit TV series about miserable rich people living in coastal California.

“I love this music. Bonnie, is this Adele?” asks Reese Witherspoon’s character, Madeline, ever-so-slightly loose from the half a Xanax she popped en route.

“No, it’s Sade, actually,” responds Bonnie.

“We should get this, honey,” Madeline says to her husband, Ed, played by Adam Scott.

“Oh, we have it,” he replies, bemused.

The joke is how much all mums love Adele. The joke is that Madeline is trying so hard to appear hip in front of her ex-husband’s younger, yoga-toned new wife. The joke is how serenely impervious Bonnie is to any back-handed compliment. The mystery is how, in a career spanning over 30 years, Sade has come to simultaneously symbolise both the dinner party-throwing pretensions of the contemptibly bourgeois and the casually classic style to which we should all aspire.

This spring, Helen Folasade “Sade” Adu, the half-British, half-Nigerian 59-year-old, is making another of her many comebacks with Flower of the Universe, her first new song for seven years, recorded for the soundtrack of the much-anticipated Disney movie A Wrinkle in Time. Announcing the coup, director Ava DuVernay wrote on Twitter: “I never thought she’d say yes, but asked anyway. She was kind + giving. A goddess … it’s a dream come true.”

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After breaking through in 1984 with first album Diamond Life, followed by another three LPs, Sade and her band (also known as Sade) took an eight-year break before returning to the limelight with Lovers Rock in 2000. There was another 10-year break before 2010’s Soldier of Love; in between, the singer granted very few interviews, all of which contributed to the image of a very private star who doesn’t “do” publicity. Fans were left to construct their own fantasy versions of Sade, based only on the music itself, plus a look described by Sade’s official website as “unspecifically exotic and effortlessly sophisticated”.

This much is consistent whichever side of the Atlantic you find yourself on, but in many other respects there has been a disjuncture between how Sade is seen and received in her homeland versus her reputation abroad. The band’s 2000 album Lovers Rock, for instance, peaked at No 18 in the UK charts, but went triple platinum in the US. When, in 2012, Sade outsold even Adele to become the highest-ranking Brit on a list of Billboard’s most profitable artists of the year, the UK press was full of baffled and dismissive references to “elevator music” and “heritage acts”. Elsewhere, her reputation has only grown, aided by an army of high-profile fans including Pink and MNEK (who’ve both covered No Ordinary Love), Nicki Minaj (who explicitly channelled Sade’s image on a recent cover shoot for New York Times Style magazine), Jessie Ware, Corinne Bailey Rae, Moses Sumney, Tinashe, Miguel (who designed a line of T-shirts with her face on them) and Jay-Z (who guested on her Moon and the Sky remix). Last summer Drake unveiled a second tattoo of her face on his lower torso.

According to Albert Watson, the noted portrait photographer and a longtime personal friend of Sade, the singer has some theories of her own on this disparity: “I said, ‘What is it with the British?’ And she said, ‘They’re tremendously supportive if you’re up and coming – nowadays, anyway – but, if you’re successful, they’re not so crazy about you.’”

It also seems that, in the UK, the smooth, soulful “sophisti-pop” sound of Sade’s music has become unshakeably associated with a particular brand of middle-class smugness with which Sade herself had little experience. Indeed, in a 1985 interview with Spin magazine, she described herself as “fairly classless, because it’s very difficult to class someone who comes from a mixed marriage. There isn’t a class structure in Nigeria [where Sade lived until the age of 11], there’s a tribal structure and prestige as far as money is concerned.”

Photograph: Sheila Rock/Rex/Shutterstock

After her parents’ separation Sade lived with her mother, a nurse, and older brother in Holland-on-Sea, Essex, before moving to London in the late 70s to study fashion design at Central Saint Martins. She supplemented her income selling clothes on a stall in Camden Market, and it was here, legend has it, that she was first approached about singing in a band. “She said, ‘Well, I don’t sing at all,’” recalls Watson, and they said, basically, ‘You must be able to – you’re black.’ Once she got going, there was a tremendous commitment, but I often wonder – if those guys hadn’t come up to her, she might have ended up being a fashion designer or something.”

Instead, Sade’s musical instinct was honed in the racially diverse London club scene of the 80s, as her boyfriend from the time, the former style journalist and current BBC Radio London presenter Robert Elms, remembers. “She was exotic in that she was always kind of preternaturally elegant,” he says, “but I don’t think the race thing was a big factor, I honestly don’t. It was a big factor in the eyes of middle-class rock writers who weren’t used to coming from council estates where half the kids had some sort of mixed-race background. It was a factor to the NME.” Elms also suggests that prevalent press attitudes to black musicians may have contributed to the ongoing undervaluing of Sade’s legacy in Britain. “The media in particular loves its black people to be tortured. Now, Sade is not tortured, and she will not do tortured for public consumption. She ain’t Billie Holiday, she sure as hell ain’t hip-hop … Sade is undeniably black; she’s African, but she’s also from Essex, and they’ve never liked that either, really. But she’s as much working-class white girl as she is African princess.”

In terms of not only nationality, then, but race and class too, a certain ambiguity seems to underpin the story of Sade’s huge, long-lasting, yet remarkably unshowy success. “Sade is one of the few people I’ve ever met who was born minimalist,” notes Elms. “Boy George you noticed, because he was flamboyant and extravagant. [With] Sade, it’s the exact opposite.” It’s this classic, understated quality that has both defined Sade’s own creative expression and made her an ideal model-muse for others. She became a regular cover star of The Face magazine in the mid-80s, and today her largely unchanged image – gold hoop earrings, red lipstick, all-seeing eyes – remains an apparently endless source of inspiration to young artists. London-based illustrator Ted Pearce, AKA Ted’s Draws, has sold out of a line of Sade T-shirts and posters, while murals of her face by street artist Dirt Cobain have been spotted all over LA and New York.

Handwritten letter from Beyoncé Knowles to Sade Photograph: Public Domain

It would be a mistake, however, to assume that this muse-like quality makes her less of a creative force in her own right; she is both muse and musician. Always has been, says Watson, who shot the iconic cover for Love Deluxe as well as several of Sade’s music videos, and counts her among the most collaborative of the many stars he’s worked with. “I mean, gigantically involved,” he recalls. “I mean, in every little detail, y’know? She’s a real perfectionist and a professional. I remember doing the first video with her, and when she came to the editing booth she had every single shot she wanted and every number of every shot … It was almost as if she created Sade and built that image around herself, but she’s actually not like the image.”

The people who know her best often speak about this contrast between the mysterious, sexy image and the down-to-earth, funny, loyal woman they know. It’s also a contrast that amuses Sade herself, Watson says. “I photograph people like Jay-Z, P Diddy, 50 Cent and they all love her! They always ask about her and say, ‘You worked with her, how is she?’ They were being real men, asking how sexy was she and so on. She’d have fallen down laughing if she’d heard that! And I told her. I said, ‘All these rappers are interested in you!’ She just said, ‘That’s nice.’”