The sign on the custard-yellow front door is an unusual one: “Chat lunatique”. When the door is opened by the feline-featured Tessa Dahl, resplendent in orange silk embroidered with parrots, it’s tempting to read something into it. But no, she bought the sign herself because it made her laugh, and because she owns seven cats.

It’s an easy mistake to make: Dahl’s mental health has never been robust. The daughter of author Roald Dahl and actress Patricia Neal, she suffered a series of tragedies in early life that sent her reeling, via depression, alcoholism, bankruptcy, drugs and a suicide attempt, to various psychiatric hospitals, ashrams and rehab clinics.

But she’s better now and, at the age of 48, finally shows signs of growing up. She is selling her home in Oxfordshire for what seem to be sound practical reasons after living in it for a respectable five years. For a woman who moved 18 times in 20 years, this is stability.

In 2000, Dahl bought the Old Forge, in the village of Wheatley, as a home for herself, her four children (by three fathers), and their nanny, Maureen Noble, who started working for the family 27 years ago, when Dahl’s eldest child, the model and writer Sophie Dahl, was just a baby. Since then, Noble has been a surrogate mother to all Dahl’s children — Sophie, 27, Clover, 20, Luke, 18, and Ned, 11 — and she’s the one who held the fort in 1997 when Dahl went bankrupt, attempted suicide and was bundled off to hospitals in Oxford, London and America for three years of surgery and addiction therapy.

“I wasn’t in my right mind,” she says. “I thought, insanely, that everybody would be better off without me, which was severely selfish. I’d been given everything, but I felt I’d blown it to such an extent I’d never recover.”

By the time Dahl returned to Britain in 1999, her children and Noble were living in a house in Clapham, south London, bought for them by her first husband, father of Clover and Luke. Ned, the baby, didn’t know his mother. Dahl moved into a B&B nearby. Within two years, she moved the family to the Old Forge. She insisted on a bedroom for everybody, including Sophie, who was already in her twenties. “When I lost my room at home it was devastating,” she says.

“My father bought me a cottage nearby in the village when I was 17 and not getting on with my mother, though I went home for every meal. We bought it for £17,000 and it has just been sold for £350,000.”

When Dahl moved to Wheatley, she was already on the road to normality, writing at the time of her peripatetic existence: “With my outstanding ability to bullshit myself, I could somehow justify the uprooting of my pets, children and stability, always sure that it would be even better than the last place. Yet I failed to realise that wherever I went I took myself with me. There is only so much running one can do.”

This time she’s not running. Despite one relapse two years ago, when a single martini led to months of rehab in Arizona, Dahl seems to be taking control. To step inside her house is to step into a feminine, well-loved retreat.

From the outside, the Old Forge looks to be a modest terraced house, albeit with a mad sign on the door. Inside, it goes on and on, with six bedrooms and four bathrooms arranged in beguiling confusion over three floors. The garden, full of Tessa’s beloved roses — she won the Green Fingers prize as a schoolgirl at Roedean — slopes steeply upwards, so her first-floor bedroom opens out on to the lawn. The walls downstairs are covered with family photographs, Quentin Blake posters from her father’s books, and pictures of animals. The bedroom walls display framed notes from the children; there are also affectionate sketches by actor David Hemmings, with whom she had an on-off affair for many years.

It’s the home of a sentimental woman, and she has put a lot of herself into it, knocking down walls, adding bathrooms, and secreting large cupboards everywhere. Delicate Victorian shell frames and glass domes display family memorabilia. Friezes of hens decorate the foot of the walls in the dining room, hot-air balloons on the walls in the kitchen. Lamps and furniture are adorned with garlands of fruit Everywhere you look there are references to her family, her childhood, animals and flowers. She’s a chain smoker, but there are no ashtrays, and everywhere smells of flowers — she uses a concierge service to keep both house and garden immaculate.

One bathroom is full of old nursery furniture from the house in Great Missenden, Bucks, in which she grew up. Her old toy chest stands in the dining room; even the bathroom tiles are from the old family home. You’d think she might want to forget a time of so much pain. At five, Dahl was pushing her brother Theo’s pram with her nanny when a taxi smashed into the pram and the baby’s brain was damaged. Then her seven-year-old sister Olivia caught measles from Dahl and died. At eight, her mother had the first of three massive strokes while bathing Dahl. Later, her parents divorced and she walked out of boarding school.

You don’t have to be a psychiatrist to spot a blueprint for trouble, but Dahl found solace when American experts diagnosed “infant post-traumatic stress syndrome”. “This affects the part of your brain in charge of emotional chemistry,” she says. “If you are constantly involved in immense trauma when very young, you become overly aware and highly strung. And this was compounded by the fact that I am a manic depressive and nobody ever realised it.”

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