So farewell then, Mary Poppins

Profound shivers must have passed through many an old-fashioned nursery last week when the Prince of Wales was photographed kissing his sons' 29-year-old nanny, Tiggy Legge-Bourke, on the ski slopes at Klosters. No mere peck on the cheek, this was an arms around the shoulder, eyes closed, affectionate kiss. But did it indicate, as some tabloids suggested, a romantic involvement? Or does it merely reflect a change in the role of the nanny?

Once upon a time, a nanny knew her place. In her heyday, between 1850 and the Second World War, the classic British nanny achieved a delicate balance between loving mother- substitute and disciplinarian within the nursery, and higher ranking servant whenthe parents were present. Nanny always knew when to withdraw. Boundaries between upstairs and downstairs, between mother and surrogate, were clearly observed.

Or so the theory goes. But even Mary Poppins, that consummate British nanny whose spoonful of sugar is now a symbol of nanny love and common sense, ended up upsetting the social order by marrying the children's widowed father.

Jane, once employed by a single father and now working for a nanny employment agency, understands. She says: "When a mother is absent through death or divorce, a growing affection is a harmless consequence of a difficult situation. You obviously get a lot closer than you would if the mother was there as well.

"After all, the father is trusting you with his most precious possessions. You are working in a home environment, you're a stand-in mum and everyone should be able to express their emotions physically. There was nothing wrong with that kiss at all. TiggyLegge-Bourke has not crossed any boundaries."

Jane is one of an estimated 30,000 nannies in this country, according to the organisation Parents at Work. Once the preserve of the upper classes, most are now employed by middle-class professionals; and while some agencies do offer male nannies, the vast majority are female and aged, on average, between 18 and 25. Their main contact where there are two parents involved, however, is not with the father, but the mother.

This is a different kettle of fish. The rivalries and competition that may emerge as two women vie to fulfil the role of mother to one child, natural to one, surrogate to the other, can create an emotional minefield. Neither has absolute authority and the balance of power constantly shifts, particularly in the case of the first-time mother. The sometimes guilt-ridden parent can be torn between an irrational jealousy of her stand-in and concern for the well-being of her child.

As Jonathan Gathorne-Hardy, author of The Rise and Fall of the British Nanny, points out, the influence of Nanny on a child's character was far-reaching. Today's parents do not want their children to grow up yearning for Nanny's reassuring, warm bosom, metaphor for the maternal love that children of the aristocracy were traditionally denied.

There is little chance of today's nannies forging the lifelong bonds that the likes of Churchill took to his grave. On the death of his nanny, Mrs Everest, Churchill mourned "my dearest and most intimate friend". Mrs Everest shared her bedroom with Churchill for the first eight years of his life. Such devoted proximity would not be considered by modern-day nannies but, like au pairs, those that "live in'' are often encouraged to become "part of the family'', to get close, but not too close.

Good, professional nannies - the ones that nanny-traumatised parents will do anything to keep - like their old-fashioned predecessors, know all about territorial boundaries and how to observe them. But as one lady-in-waiting has pointed out, Tiggy Legge-Bourke "doesn't count as a nanny, because she is a family friend. What's more, the princes are far too old to have a nanny''.

Whatever the reality of Tiggy Legge-Bourke's role and relationship to the royal household, public consternation at Prince Charles' display of affection belies a nostalgia for the mythologised nanny in uniform - the emotionally restrained, sexless figure who, in a nun-like annihilation of identity, gave up both Christian name and surname, adopting instead her employer's name.

"The old nannies were very careful not to take over from the parents," explains Lady Lloyd, daughter of the Earl of Airlie. Now in her seventies, she was brought up by a nanny, as were her own three children. "I am not very good at little children at all. My husband and I had to go on very long work trips, sometimes two months at a time, and I knew those children would be safer with Nanny than they would be with me. She would have died for them."

Today's nannies are not looking for jobs for life, says Louise Jenkinson, marketing officer of the Norland College: "The nanny working for one family for 30 years is a thing of the past. Today's nannies get married and have families of their own." That may be the case, but nannies are still expected to be committed and devoted. Quite how committed and devoted is a source of great tension.

"My last nanny, Mary, who was 18, set out to replace me,'' says Rosanne Wilson, a graphics designer with an 11-year-old daughter and seven-year-old son. "She built up an intense and immature relationship with my daughter and she herself was very juvenileand excitable. There was a sense that my daughter was being taken over.

``Nannies know you should be doing their job yourself. They know you know you should be doing it. Mary turned on the emotional screws and made me feel that I should be at home, rather than working. I felt paranoid and excluded. If I hadn't been sharing her with another mother I would have sacked her, but it was very difficult to find a rational reason to do so."

The maxim ``Nanny knows best'' hovers like an axe over parents: one false move - a pay rise denied, being late home once too often, refusing to purchase a mobile phone - and the blade falls. You are blacklisted by the nanny networks where wages are compared and horror stories exchanged in the parks and cafes , highlighted by the BBC's new drama, Tears Before Bedtime. And so the quest for the perfect nanny, the kind, loving, stimulating figure who must replace you, but not be you begins once again.

Since there is no national register for nannies - unlike childminders, they are not covered by the Children's Act - word of mouth is the only route for exasperated parents. Demand for top-of-the-range NNEB-qualified nannies trained at the Oxbridge of nursery nurse training colleges - Norland, Princess Christian or the Chiltern Nursery - far exceeds supply. Twenty Norland nurses leaving college last Christmas, for example, had a choice of some 200 jobs paying between £120 and £500 per week.

Still, 14-hour days with no extra pay, being paid in pence by the quarter-hour, having nothing to eat, being treated like a servant with no life of one's own, are common complaints. The fact that widowers think you are "fair game'', which was 29-year-oldJenny's latest experience, is par for the course." Jenny wanted to leave, but stayed for the sake of the children.

While nannies sometimes stand accused of being control-freaks bent on alienating the mother, many have the best interests of the child at heart. "After being a nanny for two months, the mother would return home from work with open arms," recalls one. "The daughter would scream, `I hate you, stay away from me, I just want to be with Sarah!' as the mother walked into the room. It is very embarrassing, particularly since you try your hardest to prepare the child for the mother's return."

Every story of the employer from hell can be bettered, in the eyes of the parents who trust a "stranger'' with their child, by ones about the nanny from hell. The nanny who force-fed the baby; the one who turned a three-year-old boy into a violent delinquent; the one who left a little boy crying in the playground after a fall, his nose pouring with blood; the alcoholic who stole money from the children's piggy bank; the one who refused to leave; the one who did leave, but with your husband - the list isnever-ending.

"Oh, for the old-fashioned nursery nanny!'' sighs the modern parent. And oh, for the old-fashioned parent and old-fashioned ways, sighs a 79-year-old former nanny who worked for two ministerial families. Of Prince Charles and Tiggy Legge-Bourke's kiss she is unequivocal: "I disapprove of such behaviour. I was never that familiar with my employer. I kept my place and they kept theirs. The family chatted to me but never put an arm around me or anything like that. It was easier that way."

All names of nannies and their employers have been changed.