Take, for example, Joan and Jackie Collins. Tonight, Joan will appear on the South Bank Show, but bonkbusting novelist Jackie won't be at her side - because Joan was reluctant to have her invited. "That's hitting below the belt, isn't it?" she snaps at Melvyn Bragg when he brings up their rocky relationship. The two finally admitted they didn't get on when Joan attempted to muscle in on Jackie's blockbuster territory. "I don't think she was thrilled when I started writing," says Joan. "We're not close now."
Other siblings who haven't found working in the same fields a smooth ride include novelists Margaret Drabble and A S Byatt. Both have explored sisterly rivalry in their novels, and Drabble has said that working in the same field did not help matters: "Things got worse when we became published writers." Liam and Noel Gallagher once claimed they fight "every day" if not "hourly"; Pat and Greg Kane of Hue and Cry were notorious for fraternal bickering long before Liam and Noel; Ray and Dave Davies could achieve nothing without a fight, according to Dave. Jacqueline du Pre's sister Hilary was a talented flautist until she was overshadowed by her more famous cellist sister; she got her revenge by writing a nasty biography. Sports commentators have suggested that tennis stars Serena and Venus Willams are spurred on by sibling rivalry. But Kate Winslet swears that her older sister Anna doesn't have any bad feelings about the fact that, while Kate stars in blockbusters like Titanic, Anna has dressed up as a pile of rubbish to teach schoolchildren about recycling, claiming they are "incredibly close".
Hmm. Siblings may find it difficult to rejoice in each other's success if they covet it themselves. Claire, in her 30s, says she is "driven crazy" by her older sister. They both work in management, but while Claire is a highly successful freelance consultant, her sister has stuck at a middling level. "I don't feel competitive at all," sighs Claire. "I just feel I've done what I wanted. But my sister will adopt a sort of elder statesman stance and say, `Mmm, well, you're going in the right direction but why don't you just ... ' and she always has to give me advice, as though she knows. I was doing a job on her level when I was 24 but that's never acknowledged." Worst of all, says Claire, she gives career advice via their mother. "She says things like `Claire should really get a new job now, before it's too late' and that gets my mum in a tizz. It drives me mad."
Even siblings who get on well admit to the odd stab of jealousy. George, 29, works in publishing. His sister works in the same field, but is, George says cheerfully, much more senior and successful. "She is an incredibly talented person who is brilliant at lots of things and I am deeply proud of her," says George loyally. "I can recall the tiniest twinge when she got a job in a specialist field that I wanted to go into. But I quickly realised this and started branching out for myself." George also acknowledges that his sister's success is not just down to luck. "She works very hard - harder than I do and harder than I am willing to do. It's not as though things have ever fallen into her lap." He does, however, wonder if he would feel differently if it was his younger sister eclipsing him. "I'm not sure if that would make me feel more jealous - she's two years older. But I certainly do look up to her, even though we are so close in age."
Strange as it might seem then, rivalry, is not automatic, even in deeply competitive professions. There really can be harmony between siblings who work in the same field. Labour Party General Secretary, Margaret McDonagh, gets on so well with her sister, Siobhain McDonagh, MP for Mitcham and Morden that they share a flat (with their highland terrier, Elvis). There is also a harmonious sister act in the House of Commons; Blair Babes Ann Keen and Sylvia Heal are siblings.
Whether siblings become rivals or support each other depends on their parents, according to Suzie Hayman, who is relationship counsellor on the BBC's The Club and also the author of You Just Don't Listen (Vermilion, pounds 8.99), a handbook for parents that aims to help them communicate with their offspring. Older children who resent younger ones and younger children constantly striving to catch up with older siblings can continue their rivalry through into adulthood, she explains. By acknowledging their children's feelings, parents can avert the worst of this jealousy. "In a family where support is offered, neither child feels as if they've lost out to another one and have to be competitive." But a certain amount of rivalry is perhaps no bad thing; there is such a thing, adds Suzie Hayman, as healthy competition.