Wearing a spray-on black catsuit, she puts her feet on the table and lies back, stretching into a supposedly feline and sexy pose. During our hour-long interview, she proceeds to demolish her parents. They are Ronald and Nancy Reagan.

Ronald Reagan’s Daughter Speaks Out. So promises the cover of Patti Davis’s book Family Secrets, another in the Mommie Dearest tradition wherein embittered children of the famous spill the beans . . . and amphetamines. She documents everything: shocking stories of her steely mother who used to hit her, sometimes daily; her own cocaine addiction and the decades of pill-popping by the former First Lady; her sexual rivalry with her insecure mother; a ‘father whose presence felt like absence’; her Dickensian toilet-training; her political activism; nights in black satin sheets with Beach Boy Dennis Wilson and her suicidal urges.

Partly inspired by Kitty ‘Kelley’s biography, it’s a decently-written book and psychologically convincing. It’s about the reality, mostly plausible, behind the facade of a ‘model family of performers’ by a woman who has had the courage to face herself in therapy. She writes about the pain of being a child in a dysfunctional family, ‘a battlefield from which no one emerged unwounded’, from the position of one who says she has learned to forgive. Before meeting her, I felt sympathy for her.

But Davis must also have been the bane of their existence. Are these just the words of a grown-up kid – a lonely, defiant, blaming and self-centred one at that – with a hostile and spiteful attitude? Why would she want to publicise private rows and expose her parents?

This, after all, is the woman who went on television in a bikini two years ago to complain about the plight of the dolphins. The one who, that same year, sold a four-page letter her father wrote to her in high school to keep up the mortgage payments on her house.

We talk about her book, for which she is reputed to have received a £300,000 advance. ‘Why should I regret it?’ she says, astounded. ‘It’s a very healing book, about someone coming from a childhood of pain to a point of forgiveness. I’m 39 and I was angry for 37 years. If I had written it before, it would have been an angry book. No, I’m not vengeful. If I were, I would have timed it to come out at election time.’

Unsurprisingly, the book has not bought her closer to her parents. The tabloids say her father has removed her from his will. (‘Probably’.) And the Reagans issued a cool official statement: ‘We have always loved all of our children, including Patti. We hope the day will come when she rejoins our family.’

One senses Patti’s emptiness as she says: ‘I think there is a lot of love in my family. We just don’t know how to communicate from that place.’ Since 1986 she has only seen her parents twice. Plus she visited her father briefly in his office in 1991 to tell him about her forthcoming book. ‘It was as if nothing had changed. He said: ‘How can you say this family is dysfunctional? It isn’t.’

‘He then showed me some pictures of me as a baby – ‘Look how happy we were’. I pointed out that I couldn’t talk yet, that might have been why everybody was so happy.’ She hoots with laughter.

They haven’t communicated since. ‘All I hear about my parents is what I see in the papers.’ She sighs. ‘I’ve no idea what’s meant to happen next and what everybody’s lesson is supposed to be. Perhaps to recognise that we don’t do very well in each other’s presence and accept that.’ She describes her father as ‘emotionally distant’ and her mother as having a ‘harsh, defensive persona’.

She is also estranged from her brother and half-siblings. ‘We were never close to begin with. Sure I’ve felt lonely sometimes. But I don’t now. It’s important to have a family, but it doesn’t have to be of people who are related to you. The people who are there for me now are Vietnam veterans, writers, actors and body-builders.’ She laughs weakly and crinkles the nose sculpted by Michael Jackson’s plastic surgeon.

Davis has long brown hair and staring eyes which she narrows in a mannerism of defiance. ‘As soon as my face starts sagging, I’ll be the first in line for a facelift.’

Yesterday afternoon she had been up for 29 hours and went to the gym instantly she got off the plane from LA. She’s addicted to weight-lifting for an hour-and-a-half a day, five days a week. She has a defensive, don’t-care attitude and it’s difficult to warm to her. But she has bursts of humour.

We return to her book. ‘What am I meant to do, pretend I wasn’t born to who I was? Writers use their lives. I didn’t write it for catharsis or a substitute for therapy. I thought it was valuable to share the emotional changes I’d made in my life.’

She also thinks it’s historically important. ‘Understanding the Reagan family might go a long way towards understanding what happened in America in the Eighties. A lot of the things I saw happen in the family happened in the country. It was a sort of drowsy decade and we lulled.’

Does she care about hurting and exposing her parents? ‘I don’t think the truth should be embarrassing, although I realise they perceive it that way. I believe in telling the truth. But that isn’t always going to be pretty. ‘Of course I care about hurting them. But I think that sometimes people choose to be hurt when the evidence doesn’t validate their pain. I think that people reading this book are going to understand them better and feel compassionate.’ She pours herself a cup of tea, sits back and doesn’t offer me one.

Did she need to wash her dirty laundry so publicly? ‘Nobody’s childhood experiences are dirty laundry. Such phrases keep people feeling ashamed and guilty about what they went through as children. People have to feel entitled to talk about whatever pain they went through so they can heal it. There is nothing shocking in this book. We all know that people get addicted to drugs and hit their children.’

Her family, she says, is no different just because it’s famous. At least she scotches the rumour that Nancy had an affair with Frank Sinatra. So what of Davis herself? A non-smoker and vegetarian, she lives in a Santa Monica bungalow with a pet squirrel and a dog. She gave up drugs in 1981, ‘toughing it out’ on her own and smoking the occasional joint to ease the ride. She has Jungian therapy once a week and has been seeing a psychiatrist ‘on and off’ for the past 21 years.

She hasn’t had a serious romantic relationship since she divorced yoga instructor Paul Grilley in 1990. ‘I love being alone. I’m too comfortable being alone. I don’t meet people because I don’t go out enough.’ Is it true her parents didn’t know she was going to marry Grilley until they read it in the papers? ‘I didn’t know I was going to marry him until I read it in the papers!’

She explains that she had done a modelling shoot for Courreges in France and put a ring on that finger. ‘I got back to the States and Newsweek had a picture of my hand with this ring on it, saying we were engaged. We looked at each other. We were already living together and we needed a toaster, so we decided to do it.’

Davis was sterilised at 24 because she was terrified of repeating her mother’s mistakes. But she has since had the operation reversed and would love to have a child. ‘I don’t find the idea of raising a child by myself frightening. If I got pregnant, I would give the man the option to have as much or as little to do with it as he wanted.’

She doesn’t think she is spiteful, selfish or bitter. (‘I was’.) And she knows she has exploited being the daughter of the ex-President. ‘It makes me more interesting, yeah.’