Who will rock the cradle?

You have to work, so someone else has to look after your children. But how can you be sure you can trust the most precious thing in your life to a complete stranger? Sally Staples says no nanny or au pair will be perfect, but offers some guidelines for finding the best help for you.

Today's nannies are not stout grey-haired figures in crisply starched uniforms pushing a Silver Cross pram through the park and teaching toddlers table manners. Now they are more likely to be Australians in jeans and trainers who will enliven your child's routine with football games, McDonalds and a lifetime addiction to Neighbours.

Thanks to the huge upsurge in numbers of working mothers, nannies are in such demand that trained ones can call the tune when it comes to employers.

There are plenty of modest couples offering a job with reasonable money and time off, but who are turned down by a nanny who can command a position in a wealthier family which includes her own flat, personal telephone line, use of the Mercedes, all living expenses paid and a salary of up to pounds 200 a week.

The rich families with two homes and an extravagant taste in holidays - which the nanny may well sample - do not necessarily make better employers but it is difficult for young girls to remain unimpressed by a glamorous- sounding lifestyle.

By the same token an untrained au pair who comes cheap is often not the wisest choice for childcare but is a real temptation for a family under financial pressure when both parents have demanding jobs and need help to look after their children.

The case of Louise Woodward has thrown the already precarious relationship of nannies and parents into something of an impasse. Employing a nanny is probably the most important decision a parent makes. They are trusting the most precious thing in their lives to a girl who is at first a complete stranger.

She may be competent and responsible. But she will not be perfect. Just as a secretary, a colleague or a friend may make mistakes, the chances are the nanny will, too. She may even tell the odd lie. If she is very young, being in charge of a toddler and a baby all day every day will test her patience to the limit. These are the facts and they are often glossed over by mothers who feel a deep sense of guilt that their children are being cared for by strangers.

And of course there are accidents. One mother vividly recalls being telephoned in the middle of an important business meeting to be told her daughter was in hospital after the nanny had shut the child's hand in the car door. This mother knew it was an accident, that it could have happened whoever was in charge and showed sympathy to the mortified nanny. But other mothers may have held an emotional grudge over the incident even though rationally they know the nanny was not at fault.

But how exactly do you choose a nanny? The cheapest way is to put an advertisement in The Lady magazine, the job-seeking nanny's Bible. The problem here is that you will have to sift through dozens of telephone calls and select perhaps six applicants for an interview.

For a busy woman this is often not possible and the current nanny is sometimes deputed to sift through the applicants for her successor - not always a happy option. Nor can the employer easily stipulate over the phone that she is averse to girls with body odour or ones who weigh in at 16 stone. When she has narrowed the field down to two or three, she will need to take up references.

The alternative is to let a nanny agency do all this for you at a cost of between pounds 300 and pounds 600. Most agencies are very good at listening to your description of the kind of girl you want. It they don't listen, try another agency.

If you believe it would complicate life having a vegetarian in your house you can tell this to the agency. If you would be bothered by a girl with green hair, tattoos and pierced nose and lip - say so. Things like this are hard to phrase in an advertisement and would make you sound like a prejudiced and fussy employer.

Many agencies run support groups for their nannies, putting girls in touch with each other if they are in the same area and inviting the nannies to report how things are going with the family. By acting as a go-between, agencies can sometimes nip problems in the bud before they grow insurmountable.

Nannies do need other nannies - even if it is only to grouse about their hours, money and working conditions - annoying for the employer but essential for the girl who needs to let off steam if she has to cope with toddler tantrums for long hours.

Lonely nannies are also vulnerable. One girl I employed from New Zealand began going to meetings at the Church of Scientology. She insisted it was only for a laugh and that she didn't believe in any of it. But the organisation played on her weaknesses and essential loneliness. Despite warnings from us, her family and other nannies, she became hooked.

Jennie Younger, Director of Investor Relations at Glaxo Wellcome, was set for a high-flying career when she began her family seven years ago. She knew her work would involve long hours and travel. She decided then that she needed to have a nanny she could rely on absolutely not only to look after the children but to run the house and on occasions organise her husband. She did not consider untrained teenagers as a viable option.

"Seven years on, Jan is still with us. She is my age, 41, and she looks after my three children. She is an absolute rock and is even moving with us from London to the country. We have been lucky but I was very specific about what I was looking for."

Once you have chosen your nanny the communication lines must be kept open. She needs the opportunity to raise problems just as much as you do. I well remember one German au pair sitting on her bed close to tears because her patience had been tried to the limit by the behaviour of my daughter who was intent on testing the new nanny to see how much she could get away with.

It was important the au pair told me this and that we made time to discuss it and ensure she would tell me if the situation was repeated. The discussion defused a potential explosion.

At least one London nanny agency boasts that it does police checks on all nannies. This may comfort a nervous employer but nothing can guarantee that a teenager, tired and frustrated with the sole responsibility of young children, will not lose her temper in a moment of anger.

Among the many nanny agencies some of the most reputable include: Nannies of Kensington (0171-937-2333), Regency Nannies (0171-225-1055) and Bellamy Nannies (0181-748-3838).