The painter Kim Noble is a niblet-sized woman with long, auburn hair and startlingly blue eyes. She lives in a small terrace house in south London with her 14-year-old daughter Aimee, two dogs and more than 100 separate personalities.

Kim, 50, has dissociative identity disorder (DID). She is, in effect, scores of different people – the exact number is uncertain – wrapped up in one body. These personalities are all quite distinct, with their own names and ages and quirks of temperament. Some are children. Some are male.

For a journalist, this presents certain problems. Kim Noble herself is merely a name on a birth certificate – a portmanteau of identities. So which version of her do you interview? Do you talk to whomever pops up? Hayley? Judy? Ken?

It turns out there's a protocol: you meet Patricia, the dominant personality among the many alter egos in Noble's head. With the help of regular support workers, Patricia looks after Aimee and makes sure there's milk in the fridge. It is Patricia who answers the door and welcomes me in.

The house is freshly painted, clean and tidy. Patricia appears urbane and at ease. She is well turned out, full of energy, just back from a holiday in Tenerife. Not a smidgen of psychiatric inpatient about her: no carpet slippers, no sad cardigans.

The photographer is setting up in the living room, so we go upstairs into Aimee's bedroom. I'm unsure how to address the person sitting on the bed opposite me. Do I call her Kim, or Patricia?

"I'm Patricia," she says equably. "I don't like being called Kim, but I have got used to it now."

How often does she change personality?

She shrugs. "There are about three or four switches a day."

What has happened so far today?

"This morning Spirit of the Water had a bath. And one of them was painting – it might have been Abi. And then the vacuum cleaning, another person was doing that before you came."

An alter ego who cleans! That's handy.

"Yeah, I have got my own cleaner," she says. "But nobody will do the garden."

The strangeness of Kim's story and something of what she has endured is revealed in her autobiography, All Of Me. The book, ghostwritten by Jeff Hudson, is a terrible tale. Kim was born in 1960. Her parents, stuck in an unhappy marriage, were factory workers, and the care of their daughter was farmed out to friends and local acquaintances. The details of what happened are hazy, but it seems that from an early age – somewhere between one and three – Kim suffered extreme and repeated abuse. And at this point her mind, traumatised beyond endurance, shattered into fragments, forming myriad separate identities. The breaks were clean: most of the principal personalities had no memories of abuse and no flashbacks. Thus she was protected from what had happened.

Kim scraped her way through childhood. Home life was fraught and she performed poorly in school. Her memory lapses and erratic behaviour were noticed but never understood. Abnormally poor memory is a classic symptom of DID. When there is a "switch", the new personality taking over does not know what has happened before they emerged. Young Kim demonstrated just such mental lacunae, and when she denied having said or done something, she was usually taken for a liar.

Did her parents never clock that something was very wrong? Patricia gives a slow blink and says, "My parents were busy."

In adolescence everything came apart. After repeatedly overdosing, Kim was placed on suicide watch in a psychiatric hospital. It was the first of many internments – each time she was released she would try to kill herself and would be readmitted. She developed anorexia and bulimia.

In her late 20s came a period of relative stability. With the immensely capable Hayley personality predominant during work hours, Kim was able to hold down a job as a van driver for five years. But one day something must have caused a switch and a disturbed personality called Julie suddenly found herself driving the van. She ploughed straight into a line of parked cars. This led to another mental health section, and a diagnosis of schizophrenia.

Eventually Kim re-emerged from hospital, and her story took another dramatic twist: somehow she found herself exposed to the activities of a paedophile ring. In the book we are told that when she reported it to the police, she received anonymous warnings to be quiet: "Threats of retaliation escalated until one day a man threw acid in her face and someone tried to set light to her bed with her in it." Kim got out, but the house was gutted.

Patricia can't remember either of these events. The first she knew of the arson attack was standing outside watching flames engulf the house. After the fire, Kim spent six months in a women's refuge. Here she became aware of the crucial, terrifying difference between her and the other residents: everyone else knew who they were hiding from. Kim could have passed her assailant in the street without realising. Something had to be done.

During this time, a new branch of mental health specialists took over Kim's care. In 1995 she was finally diagnosed with DID and began the therapy she still undergoes, without any medication. DID treatment is usually long-term and laborious – it can take years for there to be any progress. The therapist has to tease out the separate personalities and treat them individually, trying to help each come to terms with what happened in their past.

Initially – like so many of the personalities – Patricia considered the idea of DID absurd. But after six years of therapy, she finally accepted the diagnosis – and the puzzling aspects of her life slotted into place. She now understood why she always felt she was losing time, and why she had continually ended up in hospital: some of her alter egos – particularly the younger ones, frozen in time and retaining memories of abuse – were highly traumatised. Judy was bulimic. Rebecca was behind the suicide attempts. As for the acid and arson attacks, Patricia discovered they were to intimidate Hayley. She had been the informer.

Patricia cannot determine when or how often she changes into someone else. But there are triggers that are likely to set off a switch: Judy comes out at meals, Spirit of Water takes the baths. Last October Patricia and Aimee appeared on the Oprah Winfrey show and beforehand, they were filmed at home. There are some clips on YouTube: Patricia is sitting in front of a plate of food when her shoulders give a tiny jolt and she turns into Judy, a truculent 15-year-old who believes she is fat.

Each time there is a switch of personality and Patricia re-emerges, she has no notion of what has happened in her absence. So daily life is beset with lost keys, unrequested pizza deliveries, the car mysteriously parked miles from home. "I don't ever know if I am coming or going," she says. "I could switch at a door, like at the doctor's surgery, and think, 'Have I just been in?'" She shrugs wearily. "You can't ask, so I just walk off."

The other personalities have independent lives. They have their own email addresses – Patricia doesn't know their passwords; they buy clothes. Patricia shows me a large silky tent of a dress. "Does it look like me? Size 14! That'll be Judy."

Patricia is dependent on benefits, supplemented by the occasional sale of a painting. How does she – how do they – manage money? "I have control of the card and they don't know the pin number."

And what about sex? Patricia laughs. "Oh, I gave that up years ago. Any relationship like that is just too complicated."

But life hasn't always been sexless. In 1997 Kim gave birth to Aimee. The baby was immediately taken into care by social services. For years Patricia remained unaware she had a daughter.

How can a woman not realise she's had a baby?

Patricia shrugs and holds up her hands. "It was so bizarre. But there was barely a bump."

But what about the scar from the caesarean?

Patricia gestures to her flat stomach. "It doesn't show. It's mind over matter."

This might sound unbelievable but it can, in part, be explained by the fact that Kim's dominant personalities have changed over the years. Around pregnancy and Aimee's birth, Patricia was an occasional subsidiary presence. Years later, once Patricia accepted Aimee was her daughter, she instantly knew who the father was – an on/off boyfriend she'd met during her driving days. In the book she writes, "I may not have been there to give birth to Aimee, but I did conceive her." Patricia contacted the father to tell him, but he has never been involved in Aimee's upbringing.

During the pregnancy, a personality called Dawn was in charge. But following the trauma of the baby being taken away, Dawn retreated and super-efficient Hayley returned to the forefront. It was Hayley who began legal proceedings to claim Aimee back; then Bonny, a more excitable personality, took the fight through the courts.

It seems surprising that someone with multiple personalities should be trusted with the care of a baby, but Patricia says "the body" – the collective personalities of Kim Noble – would never allow Aimee to be harmed. And Kim's mind does, on occasion, possess a certain instinct for self-preservation. When eventually she was allowed to meet Aimee, only Bonny and Hayley and the other responsible front-line personalities came to the fore. After months under observation in a mother and baby unit, Aimee was allowed to live with her mother under a care order.

Everything has gone well. Two years ago, the care order was lifted, and the success of the parenting can be seen in Aimee: clever, pretty and popular, she was head girl of her primary school and is magnificently imperturbable. "It's exciting," she observes. "With other mums you have got one person. That is a bit boring." Does her mother's DID make things difficult? "There aren't many disadvantages, apart from the fact that she can't really cook, because if the oven was left on and she switched, that could start a fire."

Is the DID ever exasperating? "It can be. When I am talking to other personalities and the main personality comes, I think, 'I haven't finished what I was going to say!'"

Among the frequent personalities, Aimee can identify which is which at a glance. Some are very easy – Ken wears his hair up and has a blokeish way of pulling his shoulders back; with others the body language is more subtle. Are there any personalities she doesn't like? "There are some that come out more often, so I know them better. Judy, because she's 15, talks to me in a friendly way, like a mate. But I like them all."

The ultimate aim with DID therapy, which is not always possible and sometimes too risky to attempt, is for the patient's mind to reintegrate and become whole. Does Patricia want to integrate? She shakes her head. "My attitude is: how can I get a memory? I wasn't there, I was not in that room when that happened."

She takes me to her tiny, paint-spattered art room. It's a revelation. Since Patricia began art therapy in 2004, more than a dozen personalities have started to paint regularly and prolifically. The styles, palettes and skill levels vary enormously. Some paintings are abstract, others more representational. The paintings of Ria Pratt, a very disturbed personality, are naive little cameos with whips and cages and wispy stick figures, with the children being raped or abused painted in lighter colours.

The first of Ria's pictures was a horrible shock for Patricia. "Aimee was very little then and I had to put it away because it was quite graphic. But when I see their paintings I get excited. This is the nearest I am ever going to get to being integrated."

Dr Valerie Sinason, the psychotherapist who initially treated Kim, describes DID as "a brilliantly creative survival device". She is full of admiration for how some of her patients' personalities, having hived off the traumatised parts of their mind, can forge ahead. She believes that, like people with Asperger's, they can sometimes demonstrate exceptional powers. "They can go further than normal people because they are not held back."

Kim is a case in point. By any measure she – or rather Patricia – represents a very successful adaptation. She's managed to turn her life around, gaining considerable professional success and recognition. Patricia beams. "I am happy with everything."

• One Of Many, an exhibition of Kim Noble's artwork, opens at the Bethlem Gallery, Bethlem Royal Hospital, Beckenham, Kent on 9 November.