It's not easy being Professor Green: The rapper, the heiress and a drama made in Chelsea...

High times for the former drug dealer known as Professor Green. So why has he begun our interview with a level stare, a rub of his tattooed knuckles and a declaration that, "I'm a very angry man at the moment"?

The London-born rapper has just completed his most successful tour yet – sold out nights at London's Brixton Academy, gallons of Jack Daniel's on stage nightly, a juicy mix of pop singalongs (to accompany last year's number-one hit "Read All About It", a melodic collaboration with Brit winner Emeli Sandé) and angry hip-hop shout-outs (on "Jungle", his hymn to his occasionally troubled home 'hood of Hackney). Plus, he was joined on the road by his fragrant new girlfriend. More of whom in a minute...

He professes satisfaction that "Read All About It" settled some scores while also selling by the bucketload – "and it wasn't a fucking throwaway dance, put-your-hands-in-the-air song. Not that I'd ever make one of them."

The Prof, born Stephen Manderson to teenage parents who split shortly after his birth, directed the song at his father's partner at the time of his death: absent for much of his son's life, Peter Manderson killed himself in 2008. His new wife had publicly claimed that the then up-and-coming young musician had exploited his father's death to ratchet up publicity – an accusation that sickened Green.

"We don't have any relationship," he says of his father's widow. "And the worst thing was, I was supportive of her and her family. Even though I don't like them. I was supportive of her and her kids through [the period] when he passed away."

So, onwards with clenched jaw but bouncy gait it is. The video for Green's new single "Remedy" is hoovering up online views, courtesy, in part, of the guest appearance of BBC Breakfast presenter Bill Turnbull, an avowed fan of the platinum-selling British artist.

His new pop currency has also helped Green leverage "ambassadorship" hook-ups by the wallet-ful. He's partnered with a clutch of brands keen to co-opt some cool from the handsome, eloquent, thoughtful 28-year-old long-ago nicknamed Green on account of the colour of his preferred narcotic wares; Professor because of smarts and intelligence formed under his own steam rather than the tutelage of any educational establishment.

The ad team behind energy drink Relentless are on board. They've purloined "Avalon", a track from last year's At Your Inconvenience, to soundtrack an upcoming commercial. Ever-savvy Team Green is, in turn, using the campaign as launch-pad marketing for the fourth single from his second album.

The Puma people have hired him to front an advertising push under the slogan "The After Hours Athlete". The Danish jewellery company Shamballa is lending him all manner of shiny gewgaws. And Givenchy's Riccardo Tisci is outfitting him for red-carpet appearances. Prior to attending February's Brit Awards, the fashion brand's seamstress came to take a look at Green's inside leg, "and I never knew there was so many measurements. But she was incredible – I've never had a suit that fit so well. Black, slim-fit, two buttons, quite classic. Just really, really sharp and solid. I do feel comfortable in a suit."

Yes, he admits, he's worn a few suits before. What, to court?

"Nah," he grins, "never for court, you know. Never. I was lucky enough not to get put on that side of it. But I don't make a massive habit of it. More often than not I wear jeans and a blazer. If you wear a suit all the time it's not really an event. I don't want to wear a suit just going to the shop. I'll leave that to Theo from Hurts," he says of one half of the electro-pop duo. "He's got that look to a T."

It all adds up to a welcome rebranding for Green.

"After the first album it was all a bit novelty," he admits of 2010's Alive Till I'm Dead, a successful debut buoyed by two hit singles: "I Need You Tonight", which featured an INXS sample, and "Just Be Good to Green", which featured both a Beats International sample and a guest spot from pal Lily Allen. "People who'd heard the singles were like [withering sarcasm], 'Great, you've used big samples and you've done a song with Lily' – and that was some people's opinions of me. But I've now got rid of that. And I don't get called the 'British Eminem' as much any more.

"That's still something that people say," he allows, "but I am free of the novelty tag now. Now the only thing I have to watch is this whole celebrity thing..."

All good, right? Well, not quite. Green is as livid as the scar on his left cheek and neck, the still-raw legacy of a near-fatal stabbing with a broken bottle in an east London club in 2009.

The reason for his anger? The way his personal life has changed. When I met Green late last summer, in his flat in Bermondsey, south London, he was living with Candy McCulloch, a one-time Hollyoaks actress and the daughter of Echo & the Bunnymen singer Ian. But by the time I encountered him again earlier this year, in February, it was all change. He had moved out to Essex, but asked me not to let anyone know his precise whereabouts. He had been on the receiving end of "too much shit" in Bermondsey.

Plus, Green had swapped Candy for, well, candy. His new girlfriend was Millie Mackintosh. She's better known (in some circles) as an heir to the Rowntree Mackintosh sweet manufacturing dynasty. She's better known still (in many more circles) as one of the "stars" of E4 series Made in Chelsea. All of a sudden, Professor Green found himself one half of a celebrity couple. It's not a mantle with which he was entirely comfortable.

Still, possessed of a new suited-and-booted swagger, he professed himself more bemused than anything by a snap of he and Mackintosh seemingly out for a Valentine's Day breakfast-time promenade on the King's Road. "Man, that guy who got them photos must have been in the fucking bush!" he laughed. "Cos neither of us had a fucking clue. And my radar for that is normally pretty fucking good. I learnt a lot from Lily – she's fucking incredible, she would have seen them. Her spider sense would have gone off..."

Was that side of the celebrity circus a concern to the working-class rapper with the hard-won street-cred? It seemed not. "No, Millie and I don't really do anything wrong. We're both young and we're enjoying ourselves. There's not really that much more to it. Everyone else makes it into more."

Meeting him again earlier this month, his dog remains the same – Alfie, his powerfully built but affectionate Staffordshire bull terrier – but he has also now met Mackintosh's dogs: two "wicked" pugs called Mabel and Martha. "But they live with her parents in Bath. Martha decided to snort saliva in my face. I don't think she likes me."

Canine frostiness aside, his relationship with Millie has blossomed – as has the media circus surrounding them, not least since the beginning of the third season of Made in Chelsea. There haven't been questions in the House, but he has been discussed on-air on the reality show about posh folk and their posh lives. How has that been for him?

"Um..." he begins, his normal loquaciousness momentarily deserting him.

"Slightly embarrassing?" I suggest.

"Not embarrassing. The weird thing for me is when people who..." he begins. "If Millie's there [on the show], it's one thing if it's brought up. But it's when people discuss me and she's not even in the picture. They're people who don't know me at all. Who are they to be talking about me, least of all publicly? Yeah, I'm a very angry man at the moment," he says with a thin smile.

What's made him angry? "I don't know. I think it's the stress. I'm not gonna complain about the music business. So much has changed so quickly, again, as it always does. But it's become a real wind-up – from the minute it started, the whole class thing...

"Obviously bits of mine and Candy's relationship was in the press. But it's been completely different dating someone as in the public eye as Millie. For us, our relationship is ours. We can't help the bullshit they make up in magazines. We don't give them anything so they just literally pull stuff out of thin air. And obviously we keep it private. We haven't done our OK! shoot yet," he smirks. "Although we have been asked. Ridiculous," he tuts. "You'll never catch me in a white suit. Not even to pay for the wedding." Pause. "Which isn't in the pipeline."

He sighs. He's not one to run from paparazzi, but the intrusion is getting his goat. "It's just all the things they write and say and imply. If the difference was race or we were a gay couple, they probably wouldn't be as quick to point the difference out. But because it's class, it's fair game. That's still prejudice. You're effectively calling me a commoner – which I am, common as muck. But I'm doing all right for myself, and I'm well-mannered, I'm courteous. Which is not something that's a given for someone who has a better background. As," he sniffs, "I find out every day."

His and Mackintosh's relationship is duly boiled down: argy-bargy former drug-dealing oik meets thick-as-shit toff. "Yeah, but she's not thick as shit. And I'm a marginally decent human being. She works for her money. She doesn't live off a handout. She works fucking hard. So yeah, it's all just a bit of a wind-up."

We talk about MIA, aka Maya Arulpragasam, the London-born, self-declared agit-rapper and lyrical-terrorist of Sri Lankan heritage who repeatedly spoke out in support of the Tamil people. She then had a relationship with the son of music and drinks industry mogul Edgar Bronfman, one of the richest men in Canada. This was deemed, in some quarters, to call into question her credibility. How could MIA mean it if she'd sold out emotionally and was dating a rich kid?

"Yeah, except it's not 'sold out emotionally' because if you met someone and you get on, why the fuck shouldn't you be together?" he shoots back. "It's just weird having your fucking relationship commercialised. And there's so much other shit I'm focused on, it's not something I really want taking up headspace."

But reality – or reality TV, at least – keeps butting in. The producers have yet to ask to film Green going about his day job, or even any of his shows. But what if they did? "Nah," he says grimly. "I'm not into that. She was getting so much flak from the producers cos... like, I'd never seen an episode of Made in Chelsea until I saw the first episode [of the new series] at a screening. But as I understand it, in the second series her relationship was the focal point for the show."

Mackintosh's ex is entertainment PR, old Harrrovian and QC's son Hugo Taylor, another star of the show. "And coming out of that was not something that she was interested in having filmed again," Green continues. "And obviously I would never have it done.

"But the producers were giving it to her in the neck and I was like, 'Well, how do we resolve it? What if they see my face on camera?' So I dropped her off at a party and that was it, done, joined all the dots for them."

Green gave them a gram of flesh on the understanding that they wouldn't ask for a pound. "Which they wouldn't have got anyway. But you'd do that, wouldn't you, to make it easier for someone that you, ah, yeah..." He tails off. "I don't think they like me very much. But I'm not here to be liked, least of all by people I couldn't give a rat's arse about. They're producers of a reality TV programme so their job by nature is to sit there and manipulate people, for their own benefit, for the sake of a programme. If that's not warped, I don't know what is."

Well-built and well-tattooed but well-spoken, burdened by an unimaginably difficult childhood and youth, yet not weighed down by it, Professor Green has an upright set of morals. (OK, yes, he was a drug dealer. But that aside...) The guy who stabbed him in an unprovoked attack? A coward. Green's agreeing to give evidence against him? Doesn't make him a snitch – on the contrary, he'd be guilty of cowardice if he hadn't gone to court.

Those he loves, he loves dearly. Raised largely by women, he respects them immensely and is free of hackneyed hip- hop misanthropy. He repeatedly makes reference to his great-grandmother Edie, whose name he has tattooed on the inside of his right arm.

"She was massively important for me, along with my nan. It was her who was there when my nan was out working three jobs a day. She effectively brought me up – was the one who taught me to read. I owe a lot of my good qualities to her. A massively strong woman. And just decent. I never met my great-grandfather but after he died she never saw another man. She lived to 90 with diabetes and arthritis, through two world wars. Real fucking strength. And was still a lovely person." He was 13 when she died, "so old enough for it to really fucking hurt. That stayed with me a long, long time." His nan's name will join Edie's on his skin at some point. "And if I have a daughter I'll call her Edie, so it's two birds with one stone."

Similarly, back in February, he didn't want me to reveal the location of his Essex home – not through alertness to any lingering beefs from his time running the streets of Hackney; he just knows human nature. "It's irrespective of what I used to do. It's the fact that there are people who don't have who would like to [have]. And I've never been a thief – I've sold everything, bar crack and heroin. But I've never been a thief. I've never stolen so much as a fucking penny sweet. But because of where I come from, I have a great understanding of how people behave. People find out where you live, 'Oh, he's got a couple of kettles in his yard and there's a drought – we'll just sit outside and wait...'"

Later I wondered: was he talking about actual kettles and thirsty robbers? Or was this some drug parlance? Anyway... "That's how people behave," Green shrugged. "That's what people do to people that are even living in that same area, who aren't as successful as me."

All of which might not be such a problem these days for Professor Green. He's just moved again. For this interview we have met in his new home – a million-pound maisonette in the Royal Borough of Kensington and Chelsea. Nice views of the river, but no, I won't be more specific. Just in case.

Has Britain's inner-city poet, then, our best rapper by far, been remade in Chelsea? A year ago, would Professor Green have ever imagined he'd end up living here? "Erm... dunno," he smiles. "Probably not. Just because I never used to come out here. But it's a really nice area. The shops are wicked. There's a real... not my favourite word at the moment," he laughs drily, "but there's a real class to it. It's quite... calm's not the right word. It's not aggressive. Everyone's quite comfortable. No one's too excited. And people just get about."

But, just to set the record straight: no, there is no truth to the latest fanciful newspaper report concerning Professor Green and Millie Mackintosh. He has not moved to Chelsea to protect his girlfriend from his "abusive fans". That, he insists once more, "is bullshit".

"What I really enjoy are the eccentrics. The old English eccentrics who stand outside really nice gastropubs smoking weed." Maybe he's not that far from home after all.

'Remedy' is out on 4 June. For more: professorgreen.co.uk