AGRISLY, drizzly Monday in London. From the 16th-floor offices of the publisher Hodder & Stoughton, high above Euston Road, the city appears beautifully calm. Of course in reality it is a churning sea of individual stories, most private, some very public, but all subject to undertows of powerful emotion. This exact part of town, north of Soho, east of Bloomsbury, was immortalised by the novelist Patrick Hamilton. He wrote about the drunken denizens of pubs in the Thirties, their sexual infatuations and embarrassments, and I'm here today to meet a woman who has become just as emblematic of hedonism and heartache in our own age.

In fact, with her vintage clothes and cloche hair, Pearl Lowe could easily belong in a photograph from an earlier era, most likely by Bill Brandt, whose iconic portrait of Francis Bacon on Primrose Hill contained something of the dissolute glamour which has come to be associated with that area of London in the Noughties. Lowe is a former member of the so-called "Primrose Hill set", the hard-partying gang of actors, musicians and ace-faces that includes Kate Moss and Pete Doherty.

The scene came to national prominence in 2005 when Lowe found herself at the centre of a story alleging that she and her partner Danny Goffey had "wife swapped" with Jude Law and Sadie Frost. It was odd seeing Lowe in the tabloids. She seemed violently out of context, as though someone had torn her from an old silver gelatin print and pasted her clumsily into the News Of The World. Here was a creature of the shadows shoved, blinking and cringing, into the spotlight. "That was hideous," she shudders at the memory. "I wouldn't put that on anybody. It was quite a blow to us and our family."

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Now a fashion designer, Lowe is the former singer with Powder, a band that had some success during the mid-Nineties. "I think we were a bit before our time, and we got roped into Britpop when we were actually rock." Goffey drums and writes songs for Supergrass. The pair would be mere minor characters in the history of British music, were it not for both the "wife swap" scandal and the more recent revelation that Lowe's first-born, Daisy, a successful model, is the daughter of Gavin Rossdale, the British rock star married to Gwen Stefani.

Both controversies are covered, the latter more extensively, in Lowe's forthcoming autobiography All That Glitters. The main subject, however, is drugs. Lowe explains in great detail what it's like for a mother of three to be addicted "hopelessly and perilously" to first heroin then cocaine. She has now been clean for over two years, and can recollect in tranquillity those tranquillised years.

The point of the book is to show people, preferably other addicted mothers, that it is possible to turn your life around. She also hopes that her young children will read the book before they get to an age before they start experimenting with drugs. "I had a very bad time, and I believe I can help quite a lot of people through my misery," she says. "So I needed to be as honest as possible. There's no point doing it half-arsed, though there are maybe one or two stories that didn't make it into the book because they were too brutal."

It's hard to imagine what these might be. The book is already frank to the point of masochism, as if Lowe is punishing herself by confessing the worst in public. There's the time when Powder are due to play an important concert as part of the Reading Festival only for Lowe to discover that she is having a miscarriage; rather than cancel the show, she takes half a gram of coke, changes into a black dress that won't show the blood and performs to subsequently poor reviews.

On a later occasion, while six months pregnant with her son Frankie, Lowe attends a party in Paris thrown by someone high up in the fashion world. It is peopled by Hollywood stars, supermodels and famous designers. After dinner, lines of cocaine are brought to the table on silver trays. Clean since she learned about the pregnancy, she is unable to resist, and begins using openly at the table. Goffey has to physically pull her out of the party and back to the hotel to get her to stop.

To hear Lowe tell it, the models who persuaded her to snort the drugs were like two devils on her shoulders. "You know," she says, "I look back on that party and it was like being in hell. That's the only way I can describe it. That particular event was all about beauty and decadence. There was coke on trays, but you had to leave your soul at the door. It was hideous. I know I do not fit into that world at all. It's soulless. There's no depth. I can't be around that any more. I wouldn't even put myself in that situation now."

Lowe and her family have been living in the Hampshire countryside since August 2005. "Now the kids come home from school and run outside, when before they'd sit at the PlayStation." She has removed herself physically and psychologically from the city and its temptations, and now exists in a kind of purdah, having swapped drugs and glamorous parties for long walks and early nights. Once queen of the London party scene (or if not queen, at least some kind of debauched duchess) she now leaves her rural retreat only rarely and would probably rather not be in the capital today.

Not that she looks like anyone's idea of a bumpkin. All in black, save a pale green scarf, and with saucer eyes hovering in a storm system of mascara, she's Louise Brooks meets Edie Sedgwick. At 38, she sits like a child with her toes pointing inwards, and does not touch the bowl of strawberries on the table. It could be a symbolist painting titled Forbidden Fruit.

I ask about guilt. Looking back, how does she feel about spending nearly a decade as a drug addict while her family was very young? "Guilt is a very negative emotion," she replies, "and especially with all the work I do now, all the healing stuff, you shouldn't look back and you shouldn't regret. But I do regret not seeing my children grow up properly. I call them the missed years. Often one of them will ask, Mummy, when did I say my first word?' and I will have to tell them I don't know."

Lowe had Daisy in 1989 when she was 19. Alfie was born in 1996 and Frankie followed three years later. Following Frankie's birth, Lowe suffered from post-natal depression which she attempted to medicate with heroin. She didn't spend much quality time with her boys in their early years - "I'd always put the social situations first, as opposed to spending time with the kids" - but they are now all very close.

Since moving to the country, she has had a fourth child, born in late 2005. Betty was conceived on the day after Lowe gave up drugs for what she is determined will be the final time, and this has meant that the little girl represents something more than simply a daughter. "She's my clean child. She's my magical spirit. She's my light at the end of the tunnel." A fifth pregnancy is planned - "If I've got the energy."

Lowe spent her own childhood in the suburbs of London, near Harrow, the youngest of three children and the only girl. It was a middle-class upbringing. Her parents Leila and Eddie had a successful business in the rag trade. Lowe remembers her mother taking her to Paris to buy clothes.

It sounds like a beautiful life in the beautiful south, but it wasn't enough. She was attracted to the dark side of culture - for instance, the music of Billie Holiday and the arthouse film Christiane F, based on a true story about a young junkie. It's perhaps unsurprising that her life began to mirror art.

"I, of course, fell in with the crowd that was doing all the drugs," she says. "I was 13 and I used to score it. I remember my mum finding a packet of weed in my bathroom and just going crazy. I was a wild child, basically."

She talks about younger herself wryly, like some kind of incorrigible elder sister. Was it that she was desperate to become an adult? "In many ways, yeah. It was a love for fast things. I was friends with people who drove, so they would drive me to London and I would go to The Wag Club. I was the crazy one. People would say, Oh, she's great but she's a bit of a nutter.' So I had that reputation to live up to." It was on this scene that she first became friends with Gavin Rossdale and Sadie Frost.

Why was she the nutter though? Was it some kind of reaction against the stability of her upbringing? "I don't know if I had anything to rebel against, really... I was rebelling against myself. I did really hurtful things to myself. I have so many tattoos and hate them all. But it was just that thing of, like, I'll go and mess up my body.' I've got a massive one on my arm, one on my stomach, one on my ankle, one on my foot. It was self-destructive."

In her late teens, Lowe took a trip to Egypt and in the Sinai desert met a young American traveller called Bronner. They became a couple and set up home together back in London. They split in 1988 and he returned to the States, but Lowe discovered she was going to have a baby. "I was four months gone before I knew. I didn't show." She and Bronner decided to marry and he returned to London.

Lowe fell in love with her daughter Daisy and with the whole idea of being a mother. She felt she had a purpose in life, a new sensation. She stopped going out and taking drugs, devoting herself instead to family life. She also asked Gavin Rossdale to be Daisy's godfather.

In All That Glitters, Lowe explains that she and Bronner had a terrible relationship of constant rows, and that one night in 1988 she had sought comfort in bed with Rossdale; however, she had always believed that Bronner was Daisy's biological father. Yet Rossdale was such an unusually devoted godfather, attending all Daisy's sports days and parents evenings. Surely that's the behaviour of someone who thinks they may be the actual father?

"We always thought there was a chance, but a remote chance," Lowe explains. "In some ways it was our fantasy that he was the dad. We were so close. Best friends. So I wished he was but thought that he wasn't."

In 2003, Rossdale suggested that Daisy undergo a paternity test. He told Lowe that, as he had just married Gwen Stefani and they planned to start a family, it was time to sort this out. However, Lowe found it difficult to get him to take the test and it was eventually dealt with by lawyers. In 2004, DNA testing confirmed he was Daisy's father. There was subsequent legal wrangling over a maintenance settlement.

The whole situation has soured their friendship. Lowe says she no longer has any kind of relationship with him. "No, he won't talk to me."

Does he talk to Daisy? "He did at first, but he was always shouting at her. And then he just stopped talking to her."

Why? "I have no idea." She can't even find out via friends they have in common. "Because anybody who's associated with me he's cut off. Apparently I'm just this taboo subject he doesn't talk about."

She must be angry. "God, I've been through so many emotions. Sometimes I get so angry. Sometimes I feel pain. I think sadness is the main emotion I feel, because I've lost my best friend. And I'm sad that he can't see what an incredible daughter he's got."

How is Daisy coping? "It hurts. But she is so amazing. She has always got a smile on her face, and she's got so many friends. I've never known anyone with so many friends."

Bronner and Lowe split for good shortly after her 22nd birthday. One of the last straws came when Lowe was raped and felt that her husband gave her no support following the attack. The aftermath of the rape did, however, lead her to a career in music. Feeling a total lack of self-worth, she decided that she wanted to do something with her life that would make her daughter proud - she would become a singer. In 1994 she formed Powder. The band were taken on by the PR and management firm Savage and Best, who also handled Pulp and Menswear, and were thus well placed to surf the Britpop wave which was beginning to crest.

Lowe obviously looks back on Britpop with real fondness. Her liveliest moments during the interview come when recalling that golden period when all her friends were Top Of The Pops regulars.

"Oh, it was beyond anything I'd ever imagined in my life," she says. "It was amazing. I was going on tour with all these people I had admired - The Verve and Suede, Elastica, you name it. I played festivals where there were loads of us. Every band would arrive to play Reading on the Thursday and stay the whole weekend and there would be a massive party at the Ramada Hotel. I remember Terry Hall coming up to me and saying, You're Pearl, I love you, you're amazing.' Oh my God, can you imagine? I'd grown up listening to Specials records and fancying the pants off Terry Hall."

The whole scene was fuelled by drugs and Lowe did not say no. It was a way of fitting in. Around this time she smoked heroin for the first time and immediately knew that it could cause her problems as she liked it so much. "It's an incredible drug," she says even now. "It's the best drug." It made her feel warm and weightless and it numbed pain. Lowe has always had emotional peaks and troughs, a tendency to terrible depression and tremendous elation, and heroin initially blotted out the former while boosting the latter.

In the summer of 1995, at a festival in Belgium, Lowe met Danny Goffey and fell for him hard and fast. "He's so cocky and confident, and especially at that time as Supergrass were just about to erupt. He was younger than I was, and I didn't ever go out with young guys. I liked older men. I mean, when I was 16 I was with a 34-year-old."

Nevertheless, something clicked between them. Goffey followed her into the toilet and introduced himself. "I remember thinking, Aw, what a sweet little boy. He'll be my friend.' We ended up hanging out all day, having so much fun, and then he kissed me."

From the start, their relationship was based on drugs. They took ecstasy that first evening, cocaine the next time they met. On the day that Alfie was born, they celebrated with a line. Goffey was also one of the few people in Lowe's social circle who knew that she smoked heroin; he did it too.

At first, their drug use was fun. There was a certain innocence to it. They were two young people exploring the pleasures of life. "Definitely. I remember one time we did some acid and he made me drive to the corner shop and buy some ice cream. This was when I lived in Primrose Hill. The shop was literally five minutes away, but I must have been driving at one or two miles per hour because when we got home all the ice cream had melted. I remember us just laughing and laughing and laughing. It was mental, but those sorts of things were recurring and our life became quite difficult."

There were fissures in the relationship which drugs prised apart until they became great clefts. Lowe seems to have been insecure about Goffey's love for her, and the success of his music career cast the eventual failure of hers into sharp relief. She found it hard when he left her with the children to go off on tour, and once took an overdose of sleeping pills in an effort to get him to stay.

By the summer of 2001 she was suffering from serious depression. Goffey couldn't handle the extreme mood swings, they had terrible fights, and suddenly found themselves in a lot of debt. It was also around this time, according to the News Of The World story, that the "wife swap" took place.

How did that particular tabloid scandal affect Lowe's fragile relationship with Goffey? "It brought us closer, definitely. There were times when we lived in London when I didn't think we'd make it as a couple because of the drugs and God knows what. But I think, in a way, something bad happened to both of us and so we were together on it."

She says it forced them to talk and take stock of their relationship and lives. So it was a catalyst for change? "Yeah. It was quite poignant that time. It was the turning point for my life being great. It's funny how those sort of situations are a big blow but they make you change... and that change was the best thing that ever happened to both of us."

Why does she think she and Goffey have stayed together? "Because with Danny you never know what's around the corner. It's fun. He's an amazing father and he's very witty and very supportive. There's lots that outweighs the bad things. I think he'd say the same about me. It must have been hell living with me. I often think, Oh, you poor sod. If you'd just gone out with someone normal it would have been okay.'"

It took a lot of counselling and effort, and a few false starts, but Lowe is now drug-free. It helps that she no longer lives in London. Although famous for being a socialite, deep down she yearns for isolation. She thinks one of the reasons she was so miserable before was that she was never alone, and agrees with my theory that heroin suited her because - in its effects and because it was a shameful drug - it forced her to withdraw from the world. Heroin liberated her inner hermit.

Now she spends her days working on music (she'd love to put out a new album) and designing bespoke dresses; her clothes are available from posh London shops Liberty and The Cross, and it's her ambition to work for a major fashion company. She is touchingly insistent on her own talents as a designer and singer, no doubt aware that the excesses of her life have overshadowed the merits of her work.

Country living is not all roses. She still suffers from bleak moods, but has learned to cope with emotional pain without recourse to narcotics. "The honest truth is that the only way I've got round that depression is by reading a lot, meditating, doing things that are good for my soul - seeing healers, for instance. And I'm around nature now, which is beautiful." When she sees the flowers in her garden she experiences rushes like she used to get from ecstasy; you might call it eufloria.

What makes her so sure, though, that she will never take drugs again? "I can't be completely certain," she replies. "No one can be. But I have too many great things going on in my life for me to change.

"All I can say is: this is better, the people I have in my life are better, the situations are better. And I don't really want to go back to what's worse."

All That Glitters: Living On The Dark Side Of Rock And Roll is published by Hodder & Stoughton on Thursday, £16.99. For information on Pearl Lowe's clothes and other designs, check www.pearllowe.co.uk