British rappers do things differently these days. There was a time when the rising hip-hop star would be keen to play up their authenticity. Patrick Okogwu, 21, of Plumstead - known to the world as number one star Tinie Tempah - summons the Standard to Claridge's. For afternoon tea.

Two minutes after he breezes in, all wry self-assurance - "call me T, even my mum does, that's how bad it is" he tells me - his cousin, Dimo, a former youth worker who is now his manager, takes a call. Tinie has been invited to a Paris Hilton party in Cannes - does he want a private jet to pick him up?

Later in the day, he is due in Nottingham to support Rihanna. There is talk of D&G fashion shoots, GQ profiles. A waitress pours a couple of glasses of Laurent Perrier. Shall we?

"I'm game if you are," he smiles - and we toast his rather remarkable success.

The private jets and the champagne have come courtesy of Pass Out, the single that Tinie made with producer Labyrinth in November shortly after he signed his contract with EMI (also over tea at Claridge's, incidentally).

A wise head on young shoulders: Tinie Tempah takes afternoon tea at Claridge's

When it was released in March, its hedonistic lyrics and clever touches of ska and drum'*'bass made it an instant classic. It became the eighth number one by a solo British rapper - a remarkable stat, given that before Dizzee Rascal had his first chart-topper in July 2008, there had been none. It has gone on to clock 13 weeks on the chart (and counting), more than nine million views on YouTube, and has earned props from Damon Albarn and P Diddy.

"I never really thought number one single, I just thought this would definitely be my foot in the door. And it was in a way I could never imagine," Tinie says. Unsurprisingly, EMI suddenly has a lot riding on the young rapper from Plumstead.

When I tease him that he should actually now be enjoying, as the song suggests, groupies at his front door, he informs me that this was the case even before Pass Out. However, he continues with a sense of perspective, a level-headedness that makes EMI's investment look a wise one. His popularity among young Londoners is down to a lot more than one catchy tune.

"You get to a stage in your career when you're, like: do I go down this road and just enjoy it for what it is, or do I just try to bleach it out and focus on making it all about the music?" he reflects, sipping his Darjeeling. "I've always thought there were two types of pop stars, if you will. There's the ones that get credited for how great their music is, and how great their imagery and artistry is; then there's the ones that get credited for how much they like to party."

He wants to be in the former category - and note the emphasis on "imagery", too, an all-round approach that he has learned from American hip-hop stars such as P Diddy.

This apparent overnight success conceals years of groundwork on the London grime scene, which also spawned fellow chart-toppers Dizzee Rascal, Chipmunk and Tinchy Stryder. Tinie was originally inspired to make music when he saw the video for 21 Seconds, the 2001 hit by the London rap collective So Solid Crew, a moment many British urban artists cite as Year Zero. He was 12.

"That literally changed my whole life. Up until then, it was all about the Diddys, who seemed so far away from me. They don't know about Plumstead, they don't live in a semi-detached house like me, they don't know about my St Paul's School. But when So Solid came out - they were black, they were from south London, they knew how it was."

He began passing off their rhymes as his own in the playground, eventually saving up enough pocket money to buy a PC World microphone and experimenting with Acid Pro, the favoured software of the bedroom grime star.

He recorded Wifey, his first underground hit in 2006, bunking off school at his friend's house in Thamesmead. "We'd have to run into the garden and hide when my friend's parents came home. Happy days."

Following a positive response from friends, he hustled a pair of directors into making a video for him on a budget of £800, money he earned from a double-glazing telesales job - "I probably rang you up, and you probably told me to f**k off."

A clever clip, which culminates in Tinie accidentally running over his girlfriend, it became the most requested video on Channel U (the influential urban music satellite channel, now known as Channel AKA). Noting his younger cousin's success, Dimo managed him and localised success - and the odd well-meaning highbrow commission - followed.

However, when British rap became a commercial proposition after Dizzee Rascal's success, it wasn't enough for him. "Before you know it, those highs become lows, you hit a glass ceiling. All the gigs were at the same price, all the other artists were getting deals, our money was running out and it wasn't so much about the guy who made Wifey any more."

In a final bid for success, in 2009, he hit upon the idea of buying a video camera and starting a blog, which he called Milkand2Sugars after his love of tea. "I realised that I could get some real good behind-the-scenes footage of like, for example, a Jay Sean video shoot. I went down there with my camera, and there's Jay Sean saying, 'Yeah, Tinie's big, man.' And before you know it Jay's saying it, Chipmunk's saying it, Ironik's saying it. Then the internet went crazy."

It didn't take long for the labels to start noticing - which more or less brings us up to the EMI deal, Pass Out and talk of endorsement deals with Yorkshire Gold, his tea brand of choice.

The way he describes it - note the semi-detached house earlier - his upbringing sounds a little leafier than most grime stars. This is more down to his parents' determination than any born advantage, he stresses.

"I lived in Peckham for the first 12 years of my life and then my mum and dad decided they really didn't want to bring up their children there. So they saved up money and bought a house in Plumstead, semi-detached, three bedrooms. I remember going into it the first day and the first place I ran into was the back garden. I was saying, 'Oh shit, we have a back garden!'"

He describES a "multicultural" upbringing: "There were a lot more white people, a lot more Chinese, a lot more Asians I think that's what helped me to be as cultured as I am now." To which end he enthuses about the play Been So Long at the Young Vic and the Chris Ofili show at the Tate. He says his mother is still disappointed that he hasn't capitalised on his A-levels - Media Studies (B), Religious Studies (B), Psychology (D).

"Coming from an African background, obviously the foundation of the family home is education, probably because my parents had to work a lot harder for everything that they've got in this country [his mum works in HR, his dad is a social worker]. They fought for their position, so obviously they expect their children to make use of every opportunity that is made available to them."

His convictions come out strongest when we talk about the way young people are treated in this country. "I enjoyed my upbringing, my siblings did, we're polite, we're respectful, but at the end of the day we're young, we like to have fun. But now, more so than ever, the youth has been vilified to the point where it feels like you can't enjoy being young any more, you just have to sit it out and wait until you get old."

He agrees with my suggestion that we are frightened of young people as a society, that that fear risks turning into hatred. People are unwilling to confront bad behaviour, choosing to moan about it instead.

"I think if something is out of hand, we as a community should be able to say, you know what, mate, that's not on. And if everyone stands up and says, yeah, that's not on, you've got to stop that, they will. But we're now in a society that's become a bit Lord of the Flies. Kids think they can do what they want because adults are too scared to tell them what's right. There's not much I can do to change any of that but in the way that I can, I want to let people cling on to their youth and look back and remember it as being fun." For someone who makes pop records for a living, I reckon that is about as commendable an ambition as you can have.

In the meantime, the world is his. More than two million people have watched his next single, Frisky, on YouTube. His debut album, Disc-Overy, follows in the autumn. Naturally, he has a clothing brand to expand: "We've got some really cool T-shirts and we're thinking of branching out, making some really nice bombers and whatnot."

Then, who knows? Trying it on with Rihanna? She's taken, "unfortunately". Acting? He seems to be a natural in his videos.

"Got my Denzel Washington going on " he laughs. "I'd love to do some acting. I'd love to do everything. I just feel, I'm 21 and, thankfully, the world is at my feet at the minute." Note the prudence in his last comment, though: "I want to take full advantage of that and set myself up for as long as possible."

Frisky is released on June 7 (Parlophone)