No man is a hero to his valet; and no woman is a heroine to her children's nanny, writes Lucy Kellaway.

ROB LOWE and his wife Sheryl have been having bad luck with childcare recently. The actor, who played the gorgeous Sam Seaborn in The West Wing, has just filed lawsuits against two ex-nannies, accusing them respectively of spreading "malicious lies" and of blackmail.

In a bizarre blog last week on the website The Huffington Post, Lowe claimed that one of the nannies had demanded $1.5 million - or else she would publicise "a vicious laundry list of false terribles".

This raises all sorts of questions: in particular, how a laundry list can be vicious and what "false terribles" might be. Yet, whatever they are, there is one comforting thing about them. If a nanny spreads false terribles, you can sue and, with any luck, win.

What is more alarming is the laundry list of true terribles that nannies know. No man is a hero to his valet; and no woman is a heroine to her children's nanny.

The stars try to protect themselves against true terribles by making nannies sign confidentiality agreements. Madonna, Cherie Blair and the Beckhams have all moved to silence nannies who threatened to lift the apron on their domestic lives.

But for the rest of us nannies sit on a stack of information that has a high potential price - if not to the media, then to our employers.

Corporate recruiters seem unaware of this. If I were choosing someone for a managerial position, I would chuck out all the psychometric tests and references that reveal so little and go for the "nanny test" instead.

There is only one problem with this test - it doesn't work with people who don't have nannies or with men who leave it all up to their wives. Otherwise it is perfect.

Managing a nanny is management at its most extreme. The stakes are gigantic: getting someone else to look after our children is the biggest act of delegation that any of us ever does. You need to find someone good, you need to get them to stay, and you need to keep them happy. This isn't easy in a job that is poorly paid, has no career progression and involves much wiping of bottoms.

Any candidate who has employed a succession of nannies fails my nanny test outright and should be rejected for any managerial position. They are either bad judges of people or bad at motivation. You don't want either type as a manager in your company.

Neither would you want to employ someone who has a spying nanny cam in their house. Such a person might be fine as a compliance officer on a bank's dealing floor, but otherwise should be turned down at once.

Likewise, candidates who force their nannies to fill in time sheets saying how the baby spent every minute of the day and how much avocado puree was spooned into it should be rejected.

By contrast, those who pass the nanny test are those who keep nannies happy for a long time. A friend recently phoned to say she had just bought a dog in order to give her long-serving nanny something to look after when the children were at school. The dog had eaten my friend's favourite leather coat and shat on the floor; but she said she didn't really mind. The nanny was happy, and so it was worth it.

The nanny test proves my friend to be a woman who finds imaginative solutions to problems, who is clear about priorities and who knows how to compromise. I would offer her a top management job at the double, only she has a powerful one already.

As the developer of this test, I have made myself its first proper guinea pig. On paper, I fare very well indeed. Our nanny worked for us for 15 years and left last year only because she had moved out of London. We all loved her - both for herself alone and for her spaghetti bolognese.

Last week, I phoned her and told her about my test and asked her if she wouldn't mind commenting on my skill as a manager.

She politely hummed and hawed and, after a lot of prompting, said she didn't like the haphazard way I arranged the food in the fridge. I took this on the chin, and she added that she didn't like the way I stacked the dishwasher either. Then, emboldened, she ventured that actually she wasn't mad about the "total chaos" of the house and the way there were socks down the back of the tumble-drier.

I was a little hurt, but said never mind the socks, what about my ability as a people manager? She said she'd have a think and get back to me. A few minutes later the phone went.

"I don't want you to take this the wrong way," she said, which is never a good start. "But I think the reason I stayed with you all those years was your total lack of involvement."

I thought about it and realised she was quite right. Indeed, in a couple of seconds, my nanny test had told me something about myself as a leader. Not only do I not micro-manage, I don't macro-manage either. I recruited someone I trusted with my children's lives and I let her get on with it.

The nanny test offers conclusive proof that I am not a manager, and should be turned away if I applied to be one.