The sun is blazing hard over east London and the reigning king of UK grime is posing for pictures with his top off. Skepta’s torso is thick with tattoos; he’s got an over-sized spliff in one hand and an incongruously diddy bottle of rosé in the other. Around him, his friends and fellow MCs keep a production line of joints and jokes rolling. Kids on bikes shout greetings; passing cars bang out his current single Man (Gang). Between swigging and soaking up the sun, he’s a man at ease.

“This is my favourite photo shoot ever,” he tells the snapper. Skepta is known to be serious in interviews – solemn, even. On record he is a muscular, scowling presence, his raps a blend of brash aggrandisement, anti-establishment sloganeering and bleak introspection. Today, he’s something else entirely. He’s about to fly off to tour Australia, and his current album, Konnichiwa, has been nominated for a Mercury award. “How could I not be happy?” he says, with a rare smile.

He’s got a point. You could call Joseph Junior “Skepta” Adenuga’s rise over the last two years unstoppable. The Tottenham-born musician has captured an entire generation of young people, while taking London’s inner-city sound to the world stage. In 2016 alone, Konnichiwa entered the UK album charts at No 2, he made his Glastonbury Pyramid Stage debut and Canadian rap superstar Drake announced he had “signed” to Skepta’s Boy Better Know label in the UK. Drake sealed it by getting a BBK tattoo on his shoulder.

The path to success, however, has proved convoluted. Skepta started releasing music in the early 00s, a key figure in the grime scene that emerged when London’s sink estates started producing a dark, low-res reflection of the shiny UK garage that was dominating pop. After starting Meridian Crew (named after his Tottenham estate), then the Boy Better Know crew with his brother and fellow MC, Jamie “JME” Adenuga, Skepta became a cult underground artist. He was feted for his merciless, witty abuse of other MCs and carrying an unshakable self-determination that owed nothing to traditional musical channels in order to get his music heard.

Radio 1 doesn’t exist to me. I don’t judge my success by anything they say Skepta

“The mainstream didn’t want to hear us,” he remembers. “We knew to set up your own shit if people ain’t listening, so we were setting up little pirate stations. Pirate radio is like street art. Back in those days, when I was a kid, I thought Radio 1 just played the BBC, like if you were driving home after work and missed EastEnders, you’d be able to turn on the radio and hear it!” Even now, aged 33, that DIY mentality has stuck. “Radio 1 doesn’t exist to me. I don’t judge my success by anything they say.”

This scorn for the mainstream was exacerbated by his bruising mid-career flirtations with chart pop. Like many grime artists in the 2010s, when the industry was giddy with the bouncy chart hits of Dizzee Rascal, Tinchy Stryder and Tinie Tempah, Skepta was signed to Universal. He put out a string of singles that, while moderately successful, crowbarred him on to vapid pop-dance beats. US artists such as Puff Daddy were brought in for guest spots in an attempt to make Skepta sound like every identikit chart rapper.

Boy knows better... Skepta and members of his BBK crew in Hackney, east London. Photograph: Olivia Rose for the Guardian

But a few years of prancing around in denim vests to tunes built from C&C Music Factory samples was enough. Skepta went into a crisis of self-examination, emerging from it skint and label-less. He shakes his head at the memory: “In every area of life you get a natural talent and then somebody comes in, a manager who knows about the business, they take them and fuck them over. The talent realises they’ve been fucked over and come out the other side. Some of them fall off and some people come out untouchable. And I’m one of the people that came out untouchable. I’m winning even if I have zero pence in my bank account, because my mind’s free.”

He often speaks in hip-hop hyperbole but it isn’t without substance: since then, Skepta has achieved recognition while remaining independent. Free from label constraints, he replaced euphoric pop riffs with his own defiant productions: ice-cold electronic rhythms spiked with reggae bass and techno futurism, resurrecting the grime sound that made his name and releasing them on his own BBK label. It was the right move. In 2014, he let loose That’s Not Me, a shot of brutal energy that atoned for every misstep he’d made in the last four years in three thrilling minutes. Its video was filmed on an £80 budget and won a Mobo award. His absolution was complete. Following single Shutdown nailed his anti-mainstream stance in two blunt lines: “They try to steal my vision/ This ain’t a culture, it’s my religion.”

From there, grime went national, aided by direct-to-fan social media. In tandem with the genre’s popularity and a wealth of new MCs breaking through, Skepta’s notoriety expanded outside his core London fanbase to a new audience of suburban teenagers. His internet-enabled model, where releases would be pushed through his own channels, removed the distorting effect of major-label A&R opinion; grime could flourish as it pleased with no commercial interference. By summer 2015, the Boy Better Know crew were drawing as big a crowd at the Reading and Leeds festivals as they were at Wiley’s underground rave Eskimo Dance. Then it went global. By the time Skepta dropped Konnichiwa earlier this year, he was playing gigs from Tokyo to Lagos.

Basking in the heat, Skepta contemplates the album that’s gunning for a Mercury win. “As a younger man, I didn’t think this was possible,” he says. Its instant popularity still tickles him (all the more so as Konnichiwa was distributed direct from his home, his living room doubling up as a make-do CD warehouse). “Like, my album came out in May, I was on a flight to Toronto the next day to play a show, and they knew all the words to the new songs. The next day! You think when I was a kid I ever thought that would happen? I mean, Pharrell Williams is on my album! If I was on a major label I might think, ‘Oh yeah, that’s what happens isn’t it, I’m signed, I’ve got loads of money.’ You don’t even appreciate it. ’Cause I’m independent, I wake up every day, look in the mirror, and I’m like: ‘You! You scruffy little shit from Tottenham got Pharrell on your album! I’m blessed, bro.’ That independent existence is scary because I don’t have no certainty in my life. But that adrenaline is sick, it makes me make things happen.”

If wearing a hoodie means you’re going to rob something, I’m going to wear a hoodie and go to No 1 Skepta

The appearance of super-producer Pharrell was one of Skepta’s few concessions to the accepted wisdom of packing an album with guest spots; in contrast, the producers alone listed on the latest Kanye and Beyoncé records add up to a phone book’s worth of names. But Skepta, who produces the majority of his own music, was determined to keep Konnichiwa tight. Talk of the potential of big-name US collaborations darkens his mood.

“I had so many anti-climaxes in America,” he says. Since his star has risen in the States, numerous artists have been clamouring for a slice of Brit authenticity. But Skepta is unimpressed by their fame game. “Artists that I look up to, that I’d seen on television here in London, I meet them and they’re not even human,” he continues. “They’re just arseholes – people that, when I was younger, I thought were gonna inspire me when I met them. For real, they’ve gone too far. People tell them that they’re an artist and that they’re big and that’s what they become. I’m never gonna become the person everyone tells me I am.”

Photograph: Olivia Rose for the Guardian

This rejection of sheen over substance has been at the heart of Skepta’s comeback. These days he’s more likely to be found helping build a playground in his dad’s native Nigerian village (as he did this February) than he is to be found in the tabloid middle pages. He discarded the designer clothing he wore in the major-label years, reverting to basic black tracksuits that realigned him with the kids on the streets. (“If they paint us with the brush that means wearing a hoodie means you’re going to rob something, I’m going to put on a hoodie and go to fucking No 1,” he says). His album is full of tracks where he is the relatable everyman, from Crime Riddim’s tales of police harassment to the titular opener pointing out that he travelled “to the Brits on a train… Man shut down Wireless, then I walked home in the rain”. In keeping with this outlook, he asserts that he’d rather have a conversation with a fan than take selfies with them.

“Anyone I see in the street who asks to take a photo with me, I’m like, nah!” he says. “Instead I’ll talk to them: ‘What’s your name? How are you? What are you up to? How’s things bro?’ I’ve lived in London with no security guards for all this time, because I can’t do the celebrity shit of having security pushing people away. I don’t wanna get security, or make some fucking gold statue of myself.”

But surely if he wins the Mercury, he’ll be getting more attention? “Nah, I’m slipping back out of this,” he replies, referring to his notorious reluctance to appear in the press. “I don’t like to celebrate this shit. It’s not ungrateful, and sometimes I hear the demons in my head saying: ‘Walk the red carpet.’ But then I hear the true self say: ‘No!’” And what about the prize money? “What?” he says in surprise. “Do you get money if you win? I don’t care about stuff like that. I just wanna have enough to support my ideas, whether that means sleeping on my friend’s sofa or sleeping in a suite in the Ace Hotel.”

As he says this, as if he’s planted them there, two young fans from Aberdeen approach from the street, eager to tell him about Scotland’s growing grime scene, and how it’s spreading through online channels. True to his word, Skepta is friendly, giving them advice, genuinely listening to their responses, then resolutely refusing a selfie. They leave, starstruck and satisfied. Talk of grime spreading has the MC philosophical. “We’ve been ahead for so long in the UK, we’re so multicultural and that’s the beauty,” he says. “That’s why grime was formed, from this mix, this understanding of different people. Now other people are catching on. There’s a revolution happening.”

When Skepta talks of a revolution, he’s talking about one that starts from within. He’s a firm believer in self-actualisation, as well as the power of creating networks outside of the conventional structures. “Getting in touch with your life purpose is important,” he says, if by now a little hazily. “Now I understand what I’m here to tell everyone: togetherness is everything, bruv.”

As such, it’s little surprise that he’s got no time for party politics. Whereas some grime artists like Novelist are taking to the stage, encouraging chants of “Fuck David Cameron” and tweeting their allegiance to the Labour Party, all that is bottom of Skepta’s agenda. Last month, Tory culture secretary Ed Vaizey sent Skepta and fellow rapper Kano a congratulatory tweet for being nominated for a Mercury award. He had ignored all the non-grime artists on the shortlist in what looked like a bizarre, craven reach for credibility. Vaizey wasn’t dismissed in response; he was utterly ignored. Today Skepta has never heard of him, and has no interest in hearing about him whatsoever – Vaizey is part of a different world to his, and he sees the media and politicians as one and the same.

Skepta: ‘Greatness is a state of mind’. Photograph: Olivia Rose for The Guardian

He pauses to relight his spliff, and warms to his theme. “The other day Beyoncé was dancing to That’s Not Me in Wembley arena,” he says. “That should be on the news; that is fucking sick, it’s a game changer. But no, you turn on the TV and bam! It’s shooting guns, a bombing, everything. It’s their world, the people who are doing all this bombing and shit; politicians in the House of Commons, all these weird houses. Bro that’s their world, not mine. I don’t know them.”

He delivers this last sentence with the conviction of a charismatic leader. And why not? After breaking into the US Billboard charts, and touring the world with an album of slang-heavy music that should only make sense in the UK, you do get the feeling that Skepta could do anything with that sort of self-belief. He seems to know that, too. He taps on the side of his cap, where the word “GREATNESS” is embroidered in bold lettering.

“Greatness,” he says. “Greatness is a state of mind.”

Skepta plays Alexandra Palace, 2 Dec; the Mercury prize is on BBC4 and 6Music on Thursday 15 September