Susie Boyt: Scourge of the yummy mummy

Susie Boyt had warned me in advance that her new novel, The Small Hours, had been described as "a bit relentless". But when I finally, breathlessly, reached the final pages (yes, in the small hours), I felt exhilarated as well as chilled. Boyt's central character, Harriet, has been teetering on the brink of catastrophe, but we are left with a tentative sense of hope.

"I've got this tremendous sense of loyalty to my characters," she explains, "and with all my other books I felt I had to leave them in a better place than I found them. I deliberately set out with this book not to do that."

I meet Boyt in a cheerful café near her north London home, where she often goes to write amid the hissing of the espresso machine and the greetings of locals. "Very early on," she continues, perched neatly on the edge of a leather sofa, wearing a chic lace skirt and boots, "I wrote the phrase 'because her family didn't like her'. I wanted to investigate what that would mean, and the idea of the lost sibling."

In the opening pages, Harriet Mansfield – 38 years old, 6ft 1in, red-haired – bids farewell to her beloved therapist, Miss McGee, after years of intense treatment. Her high spirits are rendered in heightened, slightly off-kilter prose. "One of the great things about Harriet was that she allowed me to use many more words than I would normally. My other novels felt shy of using adjectives, never mind adverbs, but because she is such a red and white, stripey, blotchy person, I allowed myself to be quite indulgent." There's a good example of this on the very first page, where Harriet feels the dawn's "bright white trousers, like a sailor, hoisting her spirits even further". The dawn is in white trousers, such as a sailor would wear, but the sailor is also doing the hoisting, like a sail. It's brilliant but a bit mad, a way of signalling Harriet's perilous mental state.

"That is so not how I write and I felt daring doing it," agrees Boyt, sipping her tea, "but this is someone having her celebration leaving-home-graduation-prom-night all in one day. She's walking away thinking, 'This is it, there's no stopping me'. I did question every one of those sorts of phrases, but I felt it was her."

Harriet uses money from an inheritance to found a school for girls, a plot line that provides a shrewd commentary on current anxieties about children and schooling. Boyt was trying to find a school for her own daughter at the time, and there are helpings of satire around both Harriet's ideals and pretensions, and the yummy mummies with their "Hellman's coloured hair" and "pale grey cashmere knitwear".

Boyt, who writes a column about life and fashion in the Financial Times, signals the complex messages that carefully chosen clothes give off. (And the not so complex: one mother sports "a large diamond pavé brooch on her lapel that bore in a pretty italic script the legend Crack Whore".) Such high spirits have a serious purpose, however.

"There is a certain amount of satire about neglected rich kids," she confirms. "Well-off, lively people not really paying attention to their children – I have seen that, and it's not good enough. Neglect can be as bad as abuse. I originally had a sad scene with children being woken up for school by nannies. Somebody told me that the Filipino word for 'poopy' is 'Boris' and I wanted to get that in! But it just didn't belong," she laughs regretfully.

The Small Hours may, she points out, be the only novel ever to have been abandoned halfway through while its author wrote a book about Judy Garland. Boyt's celebrated memoir, My Judy Garland Life, mingled her own life story, tragic in parts, with a passionate account of fandom. The novel, not quite gelling, was put away for a full-scale descent into the drama of the star's life.

"Harriet had to compete with perhaps the most high-spirited, darkest person there's ever been! I also had another baby in the middle of writing it. It must have affected it massively." The novel was completely rewritten five times, and reduced by 40 per cent along the way.

Boyt describes herself as "a good Freudian" when talking about the therapy subplot, but this has a double edge. She is the daughter of the artists Lucian Freud and Suzy Boyt, and half-sister to the fashion designer Bella, the novelist Esther, and the poet Annie Freud. Did she ever feel overshadowed by her famous family? The answer is a firm no: "Because two of my sisters published novels while I was still at university, that was very inspiring – it made it seem that it was something you could do, not a wild and crazy dream," she insists. "Both my parents always worked extremely hard," and they gave her, she says gratefully, "a graft ethic".

A question about how much she resembles Harriet elicits a thoughtful pause. "I suppose I'm a dark person with high spirits, but absolutely not on that scale," she says slowly. "Unlike Judy and Harriet, I'm an extremely cautious person. I don't like people to know what I'm feeling, or even thinking. I do believe in going the extra mile in life, but I know where to draw the line. For instance, I wouldn't spend 28 hours making marzipan fruits!" She is referring to a painful, but also funny scene of Harriet's typical overcompensation in the novel. Although Boyt adds: "I've done similar things – I've made stained glass windows from Fox's Glacier Fruits."

In contrast to Harriet, with her one, grim brother, the Freud clan is huge and sprawling. "It's very deluxe having a lot of siblings," Boyt says happily. How many have you got? I venture, tactlessly. She gives a mischievous grin. "I never answer that!"

The Small Hours, By Susie Boyt

Virago £14.99

'As a woman skirted by six small children you were infinitely powerful … she was phenomenal – completed vindicated and validated by her companions ... The girls' high spirits escalated further, Harriet's rising to meet them ...'