It ain't envy. She's my sister

We're sure Jackie would have loved it." This is what an eavesdropper overheard Hilary du Pre saying at a pre-premiere showing of Hilary and Jackie, the film version of her book about her sister. But friends of the real Jacqueline say that's nonsense. She would have taken the film in the vicious spirit in which it was intended. There is little here of the joyous young virtuoso cellist who gave the world so much before being struck down by multiple sclerosis at the age of 28. Instead we see a manipulative sibling whose aim in life is to seduce her sister's husband. The portrait is so twisted, they say, that it should be renamed "Hilary's Revenge".

How could she commit such sacrilege and hope to get away with it? It's one thing to vent venom on your sister when you're still a girl, but a grown woman should at least keep her mouth shut. There's a formula for dealing with intrusive questions. It goes like this:

"Oh. Yes. Well. We used to hate each other when we were little. But now, thank God, we're the best of friends." Ask any woman over 21 how she gets on with her sisters, and nine times out of ten that's what she'll tell you. She'll be vague on the details, though. She'll claim not to remember how or why or even when things turned wonderful. She'll say, "It must have been that dreary summer in Galway, when there was no one else to talk to." Or, "I suppose things got easier after I married both sisters off to Spaniards."

Or she'll shrug her shoulders and say it just happened, and then express surprise at your surprise that an 18-year hate-fest could evolve into a mutual fan club without her even noticing. She'll go on to suggest that forgiving a sister for all the horrible things she did to you is a natural and inevitable part of growing up. But don't you believe it. To start liking a sister you once hated is the greatest feat known to womankind. It makes childbirth look easy, not to mention very short.

Even after you have your happy ending, even if your new relationship with your sister is so good that you start remembering the fun times you had together as children, and then conveniently forgot, it's still horrifying to count the ways in which the rivalry has crippled you. In my case this was literal. My sister, who is two years younger than me, also happens to be taller than me. And so my jealousy condemned me to decades of stiletto heels and platform shoes. To complete the false impression I was in the habit of buying trousers longer than my legs. This meant that I couldn't just kick my shoes off when I happened to find myself on a shingle beach, or change into trainers to go bowling. So I was always tripping and twisting my ankle.

Even in my late thirties I was still having palpitations at the very suggestion that I consider wearing flat shoes. I was still allergic to tennis and volleyball because she was so good at them, and still suffering flashes of fury at the very mention of the word "Stradivarius", because my parents had given her one when she was 12. I was still getting migraines on the nights before she came to visit, and had not yet bought her a birthday present. My alibi was always the same: every time 2 March came around, I was in bed with a high fever.

I had two children of my own before I made a connection between these fevers and the fever I was running the day my parents brought my sister back from the hospital. My parents didn't want the baby to catch it so they kept me in isolation until I got better. But not before they had proudly displayed their dread bundle and said, "Look! We've bought you a present!" A tactless introduction. But they are not to be blamed for getting my sister and me off to a bad start. As the psychotherapist Leah Potts once said, most parents don't have the faintest idea how to "help sisters be sisters".

When I think of the awful, awful things I did, I can't understand how my sister ever forgave me. She was not a saint, mind you. She was always stealing my clothes and ruining them, then having the gall to pretend it was nothing to do with her. She often pretended I had hit her, just so that my parents would punish me. But let's put this in perspective. When I was three I filled her pram with dirt, ostensibly so that I could plant a flower on her face. When I was five, I figured out how to cheat at Candyland, and didn't let her win once all summer. I can still remember her bewildered tears, and my simmering satisfaction. And the taller she grew, the greater the pleasure I took in watching her suffer. When I was a very small 12, and my sister a tall 10, I got even by exploiting her weakness for rice puddings. What I did was give her all my pocket money, so that she could double her intake and change before my eyes from a thin and pretty child into a balloon.

According to a friend who has suffered all her life under the thumb of a sister like me, Larkin had it all wrong. "It wasn't my parents who fucked me up," she says. "It was Amanda." It still goes on, even though both women are now grandmothers. They still cannot meet without things getting ugly. My friend will be sitting there, trying to make polite conversation. And Amanda will insinuate herself into the group with a simpering smile and take advantage of the first pause in the conversation to say, "Have you been to Highgrove?" When my friend snaps, "No you know I haven't, why are you asking me?" Amanda sighs and says, "Because it's such a pity you've not been asked. It's so lovely..."

Their most recent argument concerned the disposal of their mother's ashes. According to the will, this had to happen at a specific place in the wilds of Scotland. Amanda was having trouble fitting this inconvenient duty into her social whirl, and so she decided that my friend should go on her own. "But it was the way she put it that made my skin crawl. Instead of being honest, and saying she had been invited to Highgrove, she said, `I think the best thing would be if you took care of this on your own. You'd be so good at it.' I felt like saying to her, `Oh yes, I'm sure I will be. I'll bet I'll get a medal'."

My friend got even with Amanda at a cocktail party a few weeks later. This time, when Amanda asked her the Highgrove Question, as always in front of a lot of very important people, my friend said that she had never been there, and that chances were she never would. "Time is running out, you see. After all, I am 60."

Which should sound like a very mild statement - unless you know that everyone present knew that Amanda was the elder sister, and so could not possibly be 52, as she had been pretending for so many years. "I decided the time had come to blow the whistle on her," my friend told me. The dramas played out by rival sisters are full of such twists - which, of course, is what makes them so addictive and so treacherous. As Elizabeth Fischel points out in her book, Sisters, the balance of power between sisters is "in constant flux: at times, a relationship of equals, at times, anyone or the other may take control..."

When Kate Millett had a manic episode in 1973, her elder sister tricked her into visiting an asylum and then had her committed. Following another episode in 1980, her younger sister tried to do the same thing. To put all this in perspective, it may be useful to bear in mind that Kate herself once said that half her female lovers reminded her of the older sister, while the other half reminded her of the younger.

What a thought! It's little wonder that so many sisters seek protection from each other by deliberately setting out to be different. Take Gloria Steinem's sister. She's a suburban housewife and mother and she claims she and Gloria get along because neither craves the other's turf. The Mitford sisters came to a similar truce - Jessica, you will remember, became a Communist, while Diana married Britain's leading Fascist. Both Margaret Mead and Simone de Beauvoir were able to have happy, fruitful relationships with their much younger sisters by "playing mother". But what if your lives and your ambitions are too close? What does Jackie Collins think of Joan? How does Lucy Simon, the other half of the original double act, feel about her sister Carly's solo success, and how does Margaret Drabble really feel about being eclipsed by her sister?

What to make of my friend Susan's dilemma? She has tracked her estranged sister to the intensive care ward of a hospital in Australia. The sister is soon to die unless she has a bone marrow transplant. My friend Susan has offered her sister her bone marrow. But her sister so hates the thought of such a gift from her sister that she has refused it.

Her quarrel with my friend has to do with their mother's estate. Any outsider can see that there's more than enough to go round. But, of course, it's not the money that counts in these things. It's the memory of how your sister made that adorable little face, played that stinking game, and twisted your parents around her little finger to get more than her fair share of love and attention. Elizabeth Fischel calls this problem "limited resources", and you can find it at the core of just about every grievance a sister harbours against her sister.

Take my friend Janine, who was furious when her mother and sister drove 500 miles to see her, only to go into the next room to have a private giggle. How was she to know that they were planning a surprise party? As she said indignantly afterwards, "They should have told me!" It didn't even matter that their intentions were excellent. It still made her wild with anger to see her sister get something she wasn't getting. I know how she feels because once, when my sister, then about 25, woke me up to tell me that I was going to have my coffee black, as she had drunk all the milk, I sprang out of bed and tried to strangle her.

All that's in the past now. When I got divorced 10 years ago and my life fell apart, I sort of lost my authority as elder sister. And so my sister took over. She turned out to be much better at it. She's so kind to me. So wise. So much fun. So generous! I can't believe my good fortune. But it makes sense, too, that we enjoy each other's company as much as we do. After all, we have so much more in common with each other than we do with anyone else. It's been 10 years since we had anything approaching an argument. This is the most stable female friendship I've ever had, and I'm sure it will get even better as we get older.

But if she ever, ever, gets up earlier than me again and drinks all the milk...

JACKIE AND HILARY

As the classical cellist Jacqueline du Pre rose to international fame, her sister Hilary was somewhat eclipsed. Until now, that is. Her biography of Jackie, now a film starring Emily Watson, is causing something of a furore, intense sibling rivalry being the central theme. Jackie is portrayed as a manipulative, arrogant and emotionally dangerous younger sibling. No surprises that Hilary's portrayal of her younger sister may be slightly subjective. Considering that she was overshadowed sexually as well as musically, it seems, how could it be anything else? At one point in the film, Jackie declares that she wants to sleep with Hilary's husband, Kiffer Finzi. After she does just that she's heard saying, `I feel a million dollars this morning - that was exactly what the doctor ordered'.

MARGARET DRABBLE AND AS BYATT

These two novelists have elevated sibling rivalry to an art form. Younger sister Drabble's first novel, `A Summer Birdcage', looked at the relationship between two clever, manipulative sisters, whereas Byatt's 1967 novel `The Game' examined the dynamics between, yup, two sisters, one an Oxford don, the other a novelist. Drabble has admitted, `When we were little, we had just an ordinary sibling irritation. Things got worse when we became published writers.' Byatt's memory is more acidic. `I devised this technique of hitting her between the eyes on the rare occasions she banged the piano lid on my fingers.' Adulthood hasn't softened her instincts. `At the last ditch, I'm sure we'd rush to each other's help,' Byatt once said. `But at the first ditch, not necessarily.'

JACKIE AND JOAN COLLINS

Neither seems overjoyed by the other's success in film or books. When Joan became a famous actress, younger sister Jackie decided to try her luck at writing, and carved out a highly profitable career in raunchy blockbusters; `The World is Full of Married Men', `The Stud', and `Hollywood Wives'. It's when one sibling steps into the other's territory that the trouble seems to start - as when Joan decided to turn her hand to `bodice- rippers'. Jackie is rumoured to be less than happy at this sibling invasion. Still, there must have been a moment of furtive glee when poor Joan's literary attempts in `A Ruling Passion' were roundly blasted by Random House, ending up in a court case. The subject of the book? Two sisters vying for control of a small European island, naturally.

ANNA AND JANE CAMPION

`It is rather galling,' says the actress Anna Campion of the success of her younger sister Jane, director of `The Piano' and `Portrait of a Lady'. Jane achieved more than her sister from an early stage, appearing to be a more accomplished actress in school drama, and a better rider and athlete. `It was a real bore for everyone because she would win everything,' says Anna. In good sibling style, Anna followed Jane into film-directing with her extremely flawed debut `Loaded'. Anna said of Jane, `I think she wanted it to be good but not mega.' Certainly no worries on that score. Anna is philosophical about her sister's superior directing achievements. `I tend to think Jane is six films ahead, and so I just wave goodbye and think I'm on Concorde and she's on the Shuttle.'