Stella Vine is on the floor of her Bloomsbury studio, small and puckish, with her feet curled under her, showing me her sheaves of magazine cuttings, torn out scraps of inspiration.

There Stella sits, surrounded by huge unfinished canvasses of Princess Diana and Beatrix Potter, flicking through assorted leafs from National Portrait Gallery brochures and Hello! magazine. The Artist As Media Magpie, Sitting In Her Nest.

All these scraps she collected because they touched her - plucked, she says, at her solar plexus. "I will look through 200 photographs of Kate Moss and there will be just one that I connect with for some reason, maybe because of the composition or something in the eye ? Something touches me and I know I have to paint it, in the way a child knows it wants something."

Stella Vine came on to the art scene in a blaze of notoriety in 2004 when Charles Saatchi purchased her paintings of a bleeding, frightened Princess Diana, and the 21-year-old heroin casualty Rachel Whitear, displaying them in his New Blood exhibition despite censure from the public and Whitear's parents.

Stella's past added fuel to the flames. Before she started painting she was a single mother, an actress, a cleaner, a stripper, director of her own theatre company and singer in her own band. But as Germaine Greer wearily notes in her forward to the catalogue for Vine's new show: "She was and always will be the 'single mum, ex-stripper' of the art world."

It is hard to know whether it is her outsider status or her subject matter that exercises people most. She consistently flaunts demarcations between high and low culture: her latest subjects are Chelsea manager José Mourinho and his Yorkshire terrier. (She had never heard of him before, she simply liked the juxtaposition of the football manager's machismo with his race to save his little pet from quarantine.) This work, along with faux-naïve portraits of Kate Moss, Lily Cole, Liz Taylor and a suite of new Diana paintings, will form part of her forthcoming solo show at Modern Art Oxford. One critic described her appearance there as "perhaps the equivalent of Barbara Windsor starring as Rosalind in a new As You Like It at Stratford" .

Tabloids

Yet it shouldn't be surprising to see an artist truffling through tabloids. The dialogue between celebrity and art has been going on long enough, after all. Think of Joshua Reynolds and Nathaniel Hone's paintings of Kitty Fisher (actress, courtesan and Jodie Marsh of her day), of George Romney's Emma Hamilton, of Sickert's music hall stars. And then there's Andy Warhol. Stella Vine feels a strong connection there. She studied Warhol in depth on a course at Tate Modern, but she also feels she is "the same type of person as him". A part of her longs to be among the glamorous people she paints; she always felt as if "one day, I might be". Now she could be, but she is too shy to go to the parties she is invited to.

"Stella Vine paints her big-eyed subjects with as much intensity as any dazzled fan could muster and as much tenderness as if they were kittens on a chocolate box," writes Germaine Greer. "But the painted gesture is driven by something darker, something bitter."

To understand her work, some facts about Stella's life are useful. She is isolated, a loner.

"Perhaps the people I choose to paint are often objects of derision - celebrity is a bit of a put-down term, isn't it? But to me they are my world. "

Vine was abused by her stepfather as a child, and taken into care at 13. She gave birth to a boyfriend's baby - he was the caretaker of the building she lived in - at 17. She was married, very briefly, to the Stuckist artist Charles Thomson, though it ended in disaster.

"For the last few years I thought I was dirty and a hateful character, very unlovable, so I clung on to these people that I painted over and over again. Sometimes it was the places I painted, as well, often favourite romantic places, like The Priory." She refers to the celebrity addiction centre as a "favourite romantic place" without self-consciousness.

Naïve style

Stella chooses to paint in the naïve style, and sometimes she speaks in a naïve style as well, without perspective or knowingness. She is clearly extremely intelligent, and educated too, though late in life and unconventionally. (The claim that she is a self-taught painter simply means she did not go through art school - as an adult, she took classes at Hampstead School of Art and at Tate Modern, and studied Philosophical Aesthetics at Birkbeck University.)

But her view of the world is that of an outsider, unworldly; touching, as much naïve art can be, but also profoundly detached. Take this: " Shakespeare and Chantelle: I don't have more respect for one than the other. They're both human, both good people, doing what they do. I think it's easy to patronise someone like Chantelle. I watched that Big Brother quite thoroughly and I thought she was principled in the way she stood up to George Galloway, and that takes intelligence. She and Preston were more adult than the adults. So why is she not as good as Shakespeare? I mean, I know he left an incredible body of work behind ? But I think celebrities are entertaining and absorbing and I think one can learn a lot from observing other people's lives."

She knows, I think, how odd she sounds. "I feel quite ethereal, childlike, quite innocent," she says. Later she asks: "Allow me my little intelligence," sounding for all the world like John Clare. In the past she has been through periods where people - buyers, gallerists, boyfriends - have not allowed her that "little intelligence" and it stunted her. She talks of working on a portrait of Kitty Fisher and receiving a visit from a dealer who didn't seem to think much of it. After he'd gone, she ripped the canvas to shreds with a Stanley knife. She mimes the violence with passion. Those days, however, are behind her.

Androgynous

She is full of strength now. She used to be elfin and, though she would never believe it, very pretty, but she has cut her hair and put on a few stone in weight, exchanging femininity for the androgynous power of an artist. Even through the course of the interview she seems to grow stronger.

"All those people who derided me did me a favour, because now I don't care what anyone says about me. I feel I am now able to be a really powerful painter, to take on the mantle of the US male expressionist." She even compares herself to Pollock, but the way she does it is so plucky, and her defiance so hard-won, that it's hard not to feel admiring.

Stella's talent is praised by Germaine Greer, who identifies a " mysteriousness" in her way of projecting a likeness: "All the measurable details will be wrong: eye colour, hair and complexion will all be changed and yet the figure remains identifiable, as if seen through water or through a distorting glass." We recognise the celebrities she is representing, yet at the same time the figures, says Greer, become " fictitious, merely virtual". The fantasy of celebrity identity breaks down.

There is defamiliarisation at work in Vine's art, but there is also the much more traditional method of allegory. She thinks of Holbein, of George Romney, but not explicitly. She puts in whatever feels right. A robin hovers next to her likeness of Sylvia Plath, and doves around her Sharon Tate. Vine was at work on a portrait of Isabella Blow in which, in a reference to Blow's self-inflicted poison, Paraquat, weeds were going to be trailing round the frame - "a sort of Victorian poetic touch" - but she had to stop the painting half way through. "It was just too sad."

Cocaine

Vine thinks herself into the minds and bodies of her subjects - a legacy of drama school, where one of her teachers was a devotee of Stanislavsky. While working on Holy Water Will Not Save You Now, her portrait of Kate Moss, Stella became addicted to cocaine - there's Method painting for you. Explaining how painting feels to her, she becomes transported, closes her eyes: "There are zillions of pictures in your head. It's almost like you feel cold because it's night time. You can smell the night. You're there. You're THERE."

As I leave, Stella prepares to return to finishing up her suite of paintings of women who have suffered the most macabre form of celebrity: the prostitutes murdered in Ipswich last year. Their faces grin, mask-like and pretty, against a vivid forest backdrop.

"These women have been completely used, so they're almost shells. The only life force in the painting is the forest, because it carries on. They are very important to me, these paintings. Last year I was having a bad time and feeling really suicidal, and my overriding thought was, I have to finish the Ipswich girls. I can die, but I need them to be here. It always used to be my son Jamie that I thought of, but he's 21 now and he's very independent. I feel the art is my job now, my calling."

Stella shows me the pink she uses for their cartoon courtesan cheeks, raw as slapped skin. "There have been a lot of whores in art," she says, slowly, significantly. "But there haven't been many whores who have made it to the top."