Rose Boyt was 18 when she sat for her father Lucian Freud. Although “sat” is too decorous a word for this full-frontal sprawl. “Nothing had been discussed,” Boyt, a novelist, writes in the coolly explosive first line of her memoir, Naked Portrait. “I just assumed I would be naked.” She continues in the same spare, explicit style. “I got undressed and asked him what he would like me to do. He said it was up to me.

I lay down on the sofa and shielded my eyes, the big ceiling lights in the studio working on full power. I lay down, but I didn’t want to look obedient in my portrait, I didn’t feel obedient. I wanted my father to paint me but not like the others — there was some kind of battle going on, unacknowledged but expressed in the muscles of my bent leg — I was alert, prepared to spring up at any moment. I asked him not to paint in my hairy legs. He said it was not like that. We talked about make-up. He didn’t like to paint it, but I was not going to take off my mascara. In the end he decided it was part of me. That was a small victory.”

Growing up, Rose Boyt was grateful for any attention she got from her father.

I can’t think of an art book with an opening page like it. Lines land like detonations. “I was shocked when I looked at the canvas and saw what he saw.” The writing is hypnotic and propulsive, the setup compelling: father-daughter, naked-clothed, vulnerable-powerful, small victories snatched from the jaws of exposing defeat.

Freud was a famously slow painter. This wasn’t a one-off session under the studio spotlights but a campaign waged over many nights. “I sat three or four times a week, starting when it got dark, often until dawn. We were collaborators, but he always wanted to work way longer than I wanted to work — I didn’t know how to make him stop, how to stick up for myself.” Freud groaned in disappointment if Boyt needed to stretch or go to the loo. Some nights she was too tired and aching to get up from the sofa and go home. Freud chucked a blanket over her and gave her “a big glass of port to knock me out, for which I was grateful”.

Grateful. Boyt was grateful for any attention from her father; grateful for his time, for just being allowed in his life. She volunteered to clean his studio. “One way for me to make myself useful.” Washing the floorboards on her hands and knees, stooping to collect the discarded pellets of cotton wool, Boyt felt “special, downtrodden and loved for all the wrong reasons”.

I can’t think of an art book with an opening page like it. Lines land like detonations.

When the picture went badly, Freud stabbed himself in the leg with the end of his paintbrush. Boyt would lay there in silent distress as he shouted and injured himself. He picked his nose, an act for which “he seems to need an audience”. It made Boyt want to be sick. When she rang one evening to tell him she had the flu and could not sit, having staggered to a public telephone with a coat over her nightdress, he was furious.

Why did she stick at it? “When it went well he conjured a marvellous excitement under the bright lights, all the stories he told me, his escapades with aristocrats and villains in London, of his nurse and the legendary glimpse of Hitler in Berlin before he came over.” Freud, born in Berlin in 1922, the grandson of Sigmund Freud, moved with his family to England in 1933. He knew by heart Hilaire Belloc’s Cautionary Tales, TS Eliot’s “Prufrock” and Shakespeare’s Sonnet 130 (“My mistress’ eyes are nothing like the sun”), a paean to an unlovely beloved. They talked about art, analysis, Flaubert, Maupassant, Kafka and the photographs of Eadweard Muybridge.

“He seems to need an audience.” Lucian Freud, photographed by Henri Cartier-Bresson.

Freud could be endearing. When Häagen-Dazs ice cream made it to England, he became hooked on the strawberry flavor and would stand like a hungry teenager at the freezer, eating straight from the tub. Boyt would leave the studio “with so much stuff buzzing in my head I could hardly contain myself. I have forgotten any confusion or upset I might have experienced — as I remember my descent I was always elated, senses heightened, ready to take on anything under his influence.”

Freud was a charismatic monster, capricious in his attentions, bountifully selfish. He kept his many children by multiple mothers in a state of anxious uncertainty. Would he pay the bill? Would he visit on a birthday? Would he remember them at all? The painter Celia Paul, who had a son with Freud, referred to a book of Freud’s work as “Bluebeard’s Catalogue”.

The naked portrait seems the least of all evils. What gets under your skin are the small slights and omissions, the abasement he inspired in the women in his life. Rose’s mother, Suzy Boyt, made no claims on him, hid her feelings and did everything not to make him feel tied down. They met at the Slade School of Fine Art in 1956, where Freud was a visiting teacher and Suzy a student “just up from the country”. The Slade overlooked the birth of Suzy’s first child, Boyt’s older brother Ali, but when it became apparent that Suzy was pregnant again, with the baby who would be Rose, she was expelled. Freud kept his job. Suzy went on to have five children. Freud bestowed favors as and when it suited him.

Freud could be endearing. When Häagen-Dazs ice cream made it to England, he became hooked on the strawberry flavor.

This book dispels any notions about bohemian glamour. The Boyts’ poverty was terrible. Life was unsafe and unsettled. They sailed away on a cargo ship round the Baltic and, later, to Trinidad. The ship was captained by a German called Uwe who sexually menaced the young Rose.

Once, when Rose was nine, Freud took her out for tea and cakes in London. He left a big tip in coins and Boyt wondered if she could pocket them to give to her mum. It is heartbreakingly hard to read.

This book is 400 pages long. Reading the first few pages, I thought: how can Boyt possibly sustain this? It’s so powerful, so horrible, so compellingly electric. It is unsustainable. A great deal of the book is taken up with extracts from Boyt’s diaries covering the time she sat for a second portrait by Freud, a close-up head. She was often very unhappy, not without reason, and seeing, with obsessive neediness, a therapist called Bridges. The only thing worse than hearing about other people’s dreams is hearing about their therapy sessions. Boyt gives us both. Characters, important at the time of the diary, but of no interest to the reader today, drift in and out. It is like tuning into a soap you never watch. Why did no stern editor insist on cuts and compressions?

When painting went poorly, Freud would stab himself in the leg with the end of his paintbrush.

There is, at least and at last, a happy ending that makes the slog — “Felt depressed … feeling of doom … feel heartbroken … miserable … dejected, rejected, miserable” — almost worthwhile. There was a last portrait of Rose. Freud started it when she had just married Mark, a good, kind, loving widower with a young son. He continued it through Rose’s first pregnancy — “F***ING HELL,” said Freud, pleased for his daughter, but anxious for his painting — the birth of her daughter Stella, and her second pregnancy with her son Vincent. She wore a crêpe de Chine wrap-over dress over her bump and sat on the arm of Mark’s chair while Stella sat on his lap. Naked and alone no more.

Naked Portrait, by Rose Boyt, will be published by Picador on May 30

Laura Freeman is the chief art critic at The Times of London