By 2010, there will be more step-families than birth families. Are we due for a return of the evil step-mother, asks Markie Robson-Scott, or should we welcome the advent of the 'blended family'?

ALL FAMILIES are complex, and step-families are more complex than most. By 2010, the step-family will be the kind that there'll be most of. The nuclear, or birth, family will soon be in the minority. Three years ago the National Step-family Association helpline got 500 calls a month; now they're getting 500 to 1000 a week. But although this new version of the extended family, the blended family, might look fascinatingly diverse, laid- back and modern from a distance, you've only to read Other People's Children, Joanna Trollope's new novel (published on Monday by Bloomsbury, pounds 15.99) to taste the pain that has to be gone through before any semblance of inter-family fun begins.

Fairy stories about wicked step- mothers, some social historians theorise, are testimony to the very real danger once posed to the children of a first wife by the arrival of a second. When death in childbirth was common, so too were step-mothers, who would naturally want to replace the existing children with their own. Kate Saunders, whose latest novel Lily Josephine (Century, pounds 16.99) is inspired by the story of Snow White, points out that a wicked step-mother will plainly "wish for the death of an oldest son who precedes her own. The stories are frightening because small children are vulnerable and helpless especially if their natural mother has been replaced with a sort of anti-mother. For girls there's the question of sexual rivalry. Who has the greatest hold over the father? Who will win and lose that eternal battle?"

No wonder step-families are fraught with difficulty. Sending Hansel and Gretel into the forest to be done away with by their reluctant father might be a rather broad-brush representation of the problem; but can we expect the new step-families to function harmoniously when such powerful instinctual forces are at work, even if divorce has replaced childbirth as the motor force? (And as any step-mother will testify, you'd have to be a saint not to feel a twinge of jealousy about your new husband's children and a corresponding protectiveness about the rights or your own unborn offspring.)

According to a statistic arrived at by the National Step-family Association, there are 72 "pathways" into step- family life. So Joanna Trollope, a step- mother herself, can only hope to feature a tiny sample of all the possible permutations of step-relationships. But she'll have no shortage of fascinated step-readers, all curious to see how others, even fictional ones, cope. (Trollope met many step-families when researching, most of whom were happy to "let stuff pour out", which, as Trollope says, is "brilliant for novels". The most common complaints were "retrospective sexual jealousy, particularly from men - they looked at their new partner's children and couldn't bear to think back to the conception" and the lack of appreciation: "Women who said 'I still have to cook pasta for all their friends, without the dignity of being a mother'." )

On the whole, it's women who do more of the coping. "We've been together for seven years," says a divorced friend who has two children, "But my boyfriend doesn't attempt any kind of parenting role with my kids." As Gwyn Daniel, one of the directors of the Oxford Family Institute and co- author of Growing up in Step-families, says, "Men are more easily able to remain distant, though friendly, while women feel obliged to manage competently." We're brought up to feel we have to be nurturers, says Suzie Hayman, step-mother and author of The Relate Guide to Second Families, but as step- mothers we sometimes overstep the bounds in so doing: "and that can lead to resentment". Though there are no norms here: a friend (and a step-child himself), about to embark on his third marriage with three children in tow (though their main homes are with their mothers) says of his new love, "Sometimes I get the feeling that if it weren't for the kids she wouldn't bother with me."

Josie, the step-mother in Other People's Children, does try too hard to be perfect, in contrast to her new husband's chaotically undomesticated ex-wife, but she learns fast. Her three step-children hate her at first, and her own small son is badly affected by the rows and "exhausted anger" he's never experienced before in his calm former life as an only child. Things improve eventually, but before they do, Josie asks her husband's sister, "One of society's many myths is that step-mothers are cruel, but has it ever struck you that step-children can be quite as cruel as step- mothers are supposed to be?" Rather like substituting Hansel and Gretel or Snow White with The Omen. But although children may appear more powerful now that they used to, and are able, as Trollope puts it, "to throw their weight around in the family", their power is really quite limited. They didn't choose to become step-children, after all.

In the eyes of Josie's step-children, the myth of the wicked step-mother is alive and well; in her eyes, it's the kids who are being unreasonable. If you read Bruno Bettelheim (and what self-respecting New step-parent doesn't) you'll know that he thinks the step-mother myth is merely a way for a child to externalise ambivalent feelings about its real mother. It's all that good breast and bad breast stuff: a baby can't make sense of the fact that its mother is both nurturing and absent, and so sees her as two different mothers, one good and one bad. The step-mother in a fairy tale, Bettelheim believes, embodies the bad mother: and what's more tempting, for an angry step-child, than taking it literally? "You get handed your own fantasy on a plate," says Suzie Hayman. "The step- mother is a scapegoat, and sometimes people get blocked and can't move on." If a parent dies, then there's mourning and some form of closure; with the break-up of a family, the loss is still there but the grief isn't given space. Doro Marden works for Parent Network and has a grown-up step- daughter: "I'd been with her father since she was three; then her mother died when she was six. It was a terrible tragedy, and in a way worse for the child and better for the step-mother, because the relationship does become clearer. It's easier to have sole responsibility; even so it was extremely difficult."

In the past, fathers haven't helped. Growing up in Step-families, which studies 50 children born in 1958, reveals that much more was expected of step-mothers than step-fathers (still is), and that there was far more ill-feeling towards the step-mother if the father was a typically absent one who didn't know how to communicate with his children. And if a father had been an active caretaker who stopped being one when he remarried, that increased the hostility towards the step-mother. "Often it seems as if the socially constructed gender role of 'mother' took precedence over the pre-existing relationship between father and children," say the authors.

Less likely to happen nowadays, perhaps, but similar syndromes occur. One friend who took on the "mothering role" too strongly with her 12-year- old step-daughter found that "once we realised that wasn't realistic", things improved, though not till they'd had therapy. "It made the issues clearer and easier to work with. People expect the reconstructed family to behave like the primary family. But there are different rules for step- families; you need to negotiate more." Suzie Hayman says she was over- controlling during her step-son's adolescence (she'd been more like a sister figure before this, as she's only 16 years older than him). "I was expecting too much from him; it was a classic living-through-your- kids thing," which is not, of course, a neurosis unique to step-parents. Now he calls her his "significant other" and she's flattered.

Eventually, things can work well (it can take two to 10 years for a step- family to become a cohesive unit, says Cheryl Walters of the National Step- family Association, and just realising this often helps enormously), especially if the relationship between the adults is a good one. I know of one step-mother who went out to dinner with her step-daughter and the birth mother to celebrate the girl's first period - so New Age.

"I wasn't instrumental in the break-up of his marriage," says a friend who's now a second wife and step- mother, "so although things were stilted sometimes it was all right; there were no awful door-step handovers, and we never bad-mouthed the girls' mother." But nothing's perfect in life: the biological mother hasn't found a new relationship and so is "terribly there" for her daughters in a sometimes burdensome way, making visits to their father rather a relief for them. "I know I'd be jealous if my ex-husband remarried and the kids went there and had a good time," says another friend.

However, we're beginning to recognise that children can benefit from relating to other adults as well as their parents: not replacements, but additions. "A new partner is not a new parent, and any discipline needs to be given out by the birth parent in agreement with the partner, " says Cheryl Walters. "In the best circumstances, you have four committed adults, and you learn greater tolerance and skills of negotiation and compromise, while nuclear families can be very rigid."

This is the biggest growth area of family life, says Walters, making it sound like a new marketing pitch. Step-families aren't going to go away; about 3 million children will be in step-families by the year 2000. And will they grow up to be step-parents themselves? One enthusiast for the blended family whose parents have each married a number of times has 15 steps, ex-steps and half-siblings and feels himself part of the "dented fender generation. Out of this surface of chaos comes order," he says. But not everyone would agree. "Step-families can feel very lawless and lonely for children," says Joanna Trollope. The majority of step-children in the Growing up in Step-families study, says Gwyn Daniel, felt they'd never put their own children through what they'd suffered, and that their marriages were for life; if the relationship wasn't good enough to have children in, they'd leave it. But, says Walters, the big question remains: "Is it reasonable to expect two people to live together for 50 or more years?"