This being the time of year when people are hiring new nannies and au pairs, I would like to offer some words of caution: do not hire a fatty. Although it is no doubt offensive and quite possibly illegal to say so, my considerable experience of the fat ones is that they are not very good. When my daughter was about a year old, we hired a great fat girl from Northumberland. I was sceptical about having something so space-consuming and undecorative in our moderately sized house, but held my tongue. I shouldn't have, for within days of her starting work she revealed that she was a Jehovah's Witness. Quite apart from the fact that she had lied by omission in her interview, there was the concern that she might decide, according to her religion, that our daughter should not be treated by doctors in the event of an accident or illness. She assured us that she applied the rules only to herself, and we decided to let her stay. This was a mistake, for after another few months she told my wife that she was receiving psychiatric counselling relating to her unhappy family circumstances. Furthermore, she was taking my daughter, who was by now able to understand much of what she heard, along to her therapy sessions. My wife kept this information from me, knowing that I would have chucked the nanny out had I been aware of it. We let the situation drift and she munched her way along moderately competently. But when my son was born and we had a maternity nurse in the house for a few weeks, Mary Pop-it-in-her-mouth became quite seriously unhinged. She threatened the nurse, who reported it to us, and then she confided to my mother that she was feeling suicidal. Two parents of children at the local playgroup telephoned us, unprompted, to say that they were worried about our daughter's welfare in the hands of the fat Geordie, so obvious were her symptoms. I got hold of her shrink and explained all this to him, and he suggested that I bundle her into the car, drive her to the hospital and have her sectioned, which I did. A few days later she escaped and got back into our house, where she barricaded herself in her room for a week. When we eventually removed her, we found that she had staged a dirty protest, although instead of the traditional H-Block material, our nanny had smeared the walls with her favourite food, pizza. The room had to be redecorated. And our charming, utterly inoffensive cleaning lady confessed that she had been threatened and intimidated by the fat one for the previous year and a half. Four untroubled years passed with a wonderful, slim nanny, but eventually it was time for her to move on and, yet again, we plumped (pun quite intended) for a fatty, this time from the Antipodes. I took a great dislike to her, but kept my counsel for fear that my wife would think I wanted someone attractive in the house to fuel lustful fantasies, or worse. But it quickly became apparent that this girl was workshy. We took her to our Yorkshire home during the half-term holiday and, because she was new to us and the house, I decided to cook the children's and her dinner (or tea, as Australian nannies insist on calling it) on the first evening. When it was ready, I told her, expecting her to summon her charges and serve them. Instead, she sat down at the table without calling the children, picked up her knife and fork and waited to be waited upon. Her cooking was execrable, and when we told her that the children must eat fresh food rather than prepackaged microwave meals, she grumbled and whinged. One of her duties was to walk our dogs every day and this she usually accomplished in 15 to 20 minutes, including ten minutes' driving to and from the park, which is half a mile from our home. Her idea of exercising the children was hardly any better, involving as it did going to a park, sitting on a bench and telling them to go and play. On one occasion she did not walk the dogs at all, and when I questioned her about it she screamed at me that she had been too busy (her hours of work, for which she was paid £12,500 per year plus bed and board, were 8 a.m. to 9 a.m. and then 3 p.m. to 7 p.m.). So we sacked her and decided to try an au pair, whom we hired, sight unseen but with respectable references, from Germany over the Internet. She assured us that she was very energetic and that her hobbies were running, swimming and eating healthy food. In fact, she had a backside the size of an armchair, and the only food she knew how to cook was pancakes of such rich, butter-filled thickness that they defied belief. She was a vegetarian, and once I caught her feeding the children raw pork sausages because she feared that browning them under the grill might give my offspring cancer. She never swam once in the whole ten months she stayed with us, and the only time she ran was when I forced her to, because she was late for something. Quite apart from the profuse sweating and exhaustion this caused, it also brought on a fit of hysterics from which she took several days to recover. On another occasion, we hired a large girl for a few weeks to see us through a tricky holiday period. It was a time when a holistic quack had persuaded us that my daughter should eat no wheat or pork. We told the temporary nanny that this diet must be adhered to at all costs but discovered the following weekend that she had been feeding the daughter bacon butties. This could all be coincidence, but I can't help recalling the podginess of Louise Woodward, who stood trial in America a few years ago, accused of murdering the child in her care. And wasn't there a recent case in California where a fat British nanny was accused of beating the children? Of course, some thin nannies are unreliable, too, like Louise Sullivan, whom my wife, incidentally, interviewed and rejected shortly before the baby in her care died (leading to a much-publicised trial). But our experience so far leads us to be distrustful of the fat ones. Why they should be no good for the job is anyone's guess. Perhaps they are so unhappy about their appearance that they are distracted from their duties, or perhaps they are simply not fit enough to look after small, energetic, demanding children - although fat parents don't seem to have the same problem. Or maybe fat, unhappy girls are drawn to nannying in search of the happy home they might not have had. I don't know, but I insisted that our latest appointee be thin, and told my wife that we must ask applicants over the telephone, before granting them an interview, if they were fat. She was appalled and refused to ask any such thing. As it turned out, the only applicants this time round were rake-thin. Harmony has been restored to the household. Damien McCrystal is City diarist for the Evening Standard.