Jack Vettriano is moving.

We are sitting by a warm and reassuring fire in his Knightsbridge flat and studio but his London home is on the market, as is his house in the south of France. Both have been priced at millions of pounds but he doesn't know where he is going to live next. He may move south of the Thames, or back to Edinburgh, 15 years after he left the city.

We will talk about Edinburgh later, its darkness as well as its beauty. Right now, though, the painter wants to talk about Glasgow. The city is staging what he believes is a major landmark in his life and work: a sizeable retrospective of his art, with more than 100 paintings, at the Kelvingrove Art Gallery and Museum.

Now 61, the artist's hair is grey and he wears glasses. He poses professionally for our pictures. Aptly, for a morning spent with Vettriano, the urgent figures on the pristine avenue outside, in the heart of one of London's most well-heeled areas, are well dressed, vaguely glamorous, and clutching umbrellas in the rain. No butlers are singing, but the street, framed by the artist's wide bay window, is busy with au pairs from around the world, hustling uniformed children to an exclusive school.

He picks his words carefully in a mellifluous, bassy brogue. "This is the biggest exhibition of my life: you can talk to me about anything you like," he says.

I do and he replies, up to a point.

The artist, as any viewer of his art may guess, has delicate secrets. He will politely tell me when he doesn't want to speak any more on a subject. He is not an open book. But first, that exhibition: from September 21 to February 23 next year, more than 100 of his works from the last 20 years will be on display. It is, for Vettriano, an emotional moment; both a validation and a celebration of his self-made career.

He says carefully: "I don't think that it will really hit me until I walk in and see my paintings. I cannot quite visualise it. But I can't tell you how thrilled I am, and to have been approached by Kelvingrove. We didn't go hawking this around. They approached us and said: 'Look, we understand Jack must have passed his 20-year mark [of being a professional painter], and what do you think?' We jumped at the chance because, now, I have to be careful here - let's say, it didn't seem as though there was going to be an approach from anywhere else." He means, I think, the National Galleries of Scotland, with whom he has had a fraught relationship over the years. They do not own any of his work, although they recently did hang his sombre self-portrait, The Weight, in the portrait gallery.

He looks around his living room. He is wearing a pair of new, pale-rimmed glasses, a blue jacket, jeans, with a chain around his neck. The large space is usually both a studio and living room, but he has spruced it up for visitors. "The bedroom is out of bounds though - Tracey Emin ain't got nothing on my bed," he notes. There is a model of Bluebird, the landspeed record-breaking car, on one shelf, a pair of black high heels on another. On the coffee table sits an antique bust, cigarettes and lighters, as well as a DVD of David Lynch's Blue Velvet. A model of a boat sits in a glass case atop a vintage cabinet. The room is decorated with three of his larger paintings.

"This is a huge moment for me," he says. He used to work in Glasgow in the late 1980s, and used to "skive off" regularly and go to Kelvingrove. "That is where I first had the crazy notion of going into the art world. I was painting then, and I wasn't bad, but I was painting copies. I was painting little [Robert] Gemmell Hutchisons and [Samuel] Peploes and stuff. That's when I applied to Edinburgh College of Art (ECA)."

He was rejected. "Thank God, because if they had accepted me, I wouldn't be here now. I would have been beaten about the head and told to make them 'bigger, more abstract'. I was left to my own devices and gently developed this style, but I didn't know I was doing it. I didn't set out to say 'let's paint men in hats or let's do this, or that.' It was a curious thing."

The colourful and controversial life story of Vettriano has been well documented. The self-taught artist became rapidly wealthy with his depictions of women and men in night-time clinches, and distraught if often blank men in unhealthy emotional or physical situations. There are also well-dressed figures on bleached beaches, dancing to unheard music, or sun-drenched lovers on the Riviera. His detractors point to his more erotic eye: there are many paintings where scantily-clad women are placed as the objects of sexual attraction, or, in others, darkly hued rooms are inhabited by sinister men in dark suits, toying with women, under their power. Critics also point to deficiencies in technique or style. Vettriano, in the past, has seemed to care too much about his critics, and has been outspoken on his snubs from the establishment. Maybe he has mellowed - he is less keen to engage in such controversy today.

Born in Fife in November 1951, he grew up in Methil, in a modest miner's cottage. After school, he became a mining engineer, then worked in education research. But he loved art, and was intrigued by the art world. He loved looking at the paintings in Kirkcaldy Museum and Art Gallery. By the time he was rejected from the ECA, he had taken on his mother's maiden name (he was born Jack Hoggan) and his two first publicly available canvases, for the Royal Scottish Academy show in 1989, propelled him on a rollercoaster ride of competing galleries, exhibitions, escalating prices, record-selling prints - his ubiquitous The Singing Butler has sold 10m copies around the world - healthy royalty cheques, a few expensive houses, and a few interesting stories along the way. His original paintings, he says, were probably inspired by his father's friends coming to the house, smartly attired, and his mother's friends "with all their nylons on", as well as the Art Deco interior of the Raith Ballroom in Kirkcaldy. He says: "The principal driving point in my compass has always been women. The first two paintings I did, one was one called Saturday Night, based on the ballroom in Kirkcaldy, and the other was a woman in a white slip. They both sold. I got approached from three galleries and it kicked off. But if you had said to me then: 'Kelvingrove in 20 years, what do you think?' I would have said: 'Go and get your head looked at.'"

He believes the public will be able to scan the changes in his art as they work their way around the show. Vettriano takes his job very seriously. He acknowledges past technical failings, but adds: "I used to look back at the early works and think, 'I can't believe I did that' but now I think they have a charm, because they were the best I could do at the time. That's the point about the journey - and that is what people will see. They will see the hats starting to come off, dresses getting a bit more contemporary, and then there's a whole period of sexual stuff, and the beach period. So they will be taken on a journey through my mind. I was looking at some the other day and I was thinking 'Of course I could do that better now, but I am 20 years bloody older.'"

Vettriano will shortly be making more journeys. He may return to Edinburgh, he says, and will view some properties. But he seems a little nervous. He had a dark and hedonistic period in the 1990s.

He says: "I loved Edinburgh. It is wonderful, but it has an underbelly... that I never quite managed to come to terms with." He used some of it for material, including painting scenes inspired by the Scorpio Leisure sauna in Leith. Some of the women there visited Vettriano's studio to pose for paintings, while at other times he would work from photographs he took there. He gave the owner of the sauna some paintings as a gift, and they recently made the news pages when seized by the police.

He says: "I can look at any painting and know where I was, who I was seeing - which is generally quite significant - the music I was listening to … I can tell you pretty much, within a week or two or a month."

His mind turns to his erotic, or darkly, sexually-charged paintings. They always sell well, but have also proved controversial. The artist leans forward in his armchair - he has a point to make. "It worries me sometimes that critics think that I get a sexual thrill from my paintings. I don't. Because I have been there. I have been in those paintings. And it's not any fun. I could go through 20 paintings with you where [in reality] it has ended up disastrously."

He once said his paintings had been inspired by "25 years of sexual misbehaviour". He sighs. "I went through a period of hedonistic stuff in Edinburgh. And I painted this picture, Beautiful Losers." It depicts two men and a woman. "I called it that because, yes, they are beautiful, they have money, they can drink champagne but ultimately, they are losers. Because nobody wins in a threesome. You know, it just doesn't work." He adds: "I went through these periods ... bondage and stuff like that. I don't regret those periods. Up until I was 40, I was a sort of corporate guy, but by the time I was 45 I had made not a little bit of money, and I had this need to be hedonistic."

No, he replies to my question, it was not a reaction to his childhood, but "a reaction to spending 20 years of my life, working for somebody else, paying a mortgage, having money to eat out only once a month. I think it was simply that I got introduced to things ..." He seems to flinch, remembering those times. "It came to an end. It came to a very abrupt end. I will never tell the story, because I can't. I am glad it did, because I think ... I think I'd had enough, but I don't think I realised I'd had enough.

"Curiously enough, when I came to live in London, people would say, 'Oh, you're an artist, you want to live in a loft in Soho, or you want to be in Notting Hill.' But I said, 'No, I don't want to be anywhere near there. I want to live in a civilised area where there are no girls on the streets, or drugs being sold. I had just had it."

That exhaustion and regret is depicted in his self-portrait, The Weight, which will be at Kelvingrove. He says, at a push, that The Weight is "as good a painting as I have done". He adds: "I do suffer from depression. And melancholy ... I have dabbled in therapy, but I don't know, it's become too fashionable and too expensive. I think what you need is a good friend, or a good girlfriend."

Does he have one at the moment? "Yes, I have been seeing her for about a year. She is good for me, she doesn't let me away with things." Would he marry again? He has been married before, and divorced. "I don't know about that. I am quite happy with our relationship, and there is no f****** about, like I have done in the past."

He adds: "There is a lot of regret. Regret in the sense that I think I was very careless, and I don't think that being careless is fun, when you hurt other parties. But not only other parties, but other parties' other parties."

Vettriano knows the retrospective will open his art up for public and press inspection on a larger scale than ever before. "I will get flak," he nods. And, although he can be articulate about his painting in a personal situation, he admits he has found it difficult in public settings.

He says: "There's a funny thing. Because some people absolutely abhor my work, and there are some people who absolutely love it. I have this terrible fear - I think it's a working class thing - of having to defend myself at a dinner table."

But he adds: "I don't buy into the view that anything popular has anything to do with bad taste or cheapness. If something is popular, it's popular for a f****** reason. And to have sold 10 million copies of The Singing Butler worldwide is no mean feat. I think that regardless of what the critics say, the way that I composed that picture, I deserve some credit."

The Singing Butler sold at auction for £744,500 in 2004. "It still sells very well [in print form]. It seems to inspire people: I have had three film scripts based on it sent to me. Two of them are just Mills and Boon, the third one...the butler is having intercourse with the wife, the maid and the husband! And then he kills the husband."

He has fans in high places, too. Collectors and collaborators have included Terence Conran, Italian photographer Fredi Marcarini, Sir Tim Rice, Sir Alex Ferguson, Sir Jackie Stewart, and Scotland's First Minister Alex Salmond, with whom he designed a charity Christmas card.

Vettriano may move back to Scotland but won't be drawn on whether he will vote Yes or No in the independence referendum. "I am not a political animal. I did some work with Alex Salmond, and we had a great time. I think he cares deeply for Scotland."

He adds: "What I do like is that he wipes the floor with Holyrood. There is no one with the wit like him. As I say, politics? Not interested. But I like the guy. He has defended me and I am grateful for that."

In 2009, Vettriano launched his own company, Heartbreak Publishing, and his own London gallery, also called Heartbreak, which represents him. Right now, however, he cannot think of what he will create next.

He will not retire any time soon. "A man needs to work. What would I do all day? Leonard Cohen in a poem, about pornography [Recitation], says 'I am old, but I am still into that', and I am a bit like that. I am the same, I am old, but I will never change that need."

It is time to leave. Perhaps Vettriano should be more open about some of his secrets: one of them is hanging on the wall next to his kitchen. It is a stark and arresting self-portrait. It is an almost brutal image of distressed man. A smudged panel of words hangs behind the figure. I assumed the painting is not by Vettriano's hand. But it is. As we depart, the artist says: "Yes, it is stark. It is meant to be. It's not been shown in public." What does the writing say? He pauses and says, with rumble: "It says: 'What does it profit a man if he gains the world - but loses his soul?'" n