Are you brave enough to share

There are many things you can do to offend another family during a shared holiday. Nicking the best bedroom. Quibbling over restaurant bills. Getting off with the other person's husband.

Or you can do what I did and feed their six-year-old's surprise homemade birthday cake to your children by mistake. (It was in the fridge when we arrived. My children were hungry. The other family was asleep. I thought it was one of those little offerings you find welcoming you in rented cottages. I was to regret this mistake deeply the morning after.)

A shared holiday with another family sounds like a brilliant idea when it is first conceived - over dinner, say. It seems like the perfect solution: entertainment for the children, company and conversation for the grown-ups, shared cooking, shared help, shared experiences, the chance to rent a bigger, nicer house that you might not be able to afford on your own. (It's extraordinary how many people use that last one as a reason. Why? You could do that in your real life. But in real life you value your privacy and you don't.)

In a recent poll for Toluna, an opinion website, more than half of recipients who answered 'yes' to having gone on holiday with another family, added, 'but never again'. And most of us have stories, or know people who have stories, of when it all went horribly wrong.

"We would never have dreamed of going on holiday with anyone else before we had kids," Elsa Morris, a mother of two young daughters, told me recently. "I mean, why would you want to? But now, suddenly, I can see the point. Last year, we went to a villa and it was lonely.

"It was Keith and me and the kids. It was a long, long, hot, boring day. And the girls missed their friends and their toys ... So, yes, this year, we are taking the plunge. We're renting a house in France with some friends who have kids in the same nursery. They are bringing their au pair, so hopefully we'll have more of a rest. I'll let you know how it is when we get back."

You just know, don't you, that it's not going to be all roses? Their au pair? That's a disaster from the start. "Never go with the other family's au pair, maid or nanny, unless you are bringing one of your own," says Helen Irvine, a psychotherapist and mother of three.

"Of course, their maid won't want to look after your children and your children won't want to be looked after by them. You'll end up in the pool, or playing Lego with your children and theirs, inwardly seething as you watch your friends relaxing on their day-beds."

My friend Elsa has something else stacking against her - the children are nursery age, and it is in this age group that you find the highest cluster of horror stories.

Parents, anxious or insecure, still think it matters how many ice-creams their children have before lunch. "That terrible double conversation you have with your own kids," says Irvine.

"'No, you can't have a lolly yet.' 'But, Mum, you said ...' And you can see the other mother grimacing." Or they might not yet have learned that very important life lesson: that no one else cares how clever, or talented, or advanced their own child is. "Oh look," mimics Sacha Jones, a teacher with a nine-year-old son. "'Look at clever Effie with her little bucket and spade?' Oh go away." It takes a bit of time, too, to learn when it is acceptable to tell off someone else's child: never.

Irvine adds: "By day three of a shared holiday, an infant's sleeping routine can represent an entire moral code. We had a nightmare once with another couple in Corfu. They were all, 'Oh no, we can't possibly go to the beach for lunch, little Felix has a nap between noon and 2pm.' We were thinking, 'Oh, how ridiculous, our whole day is being dictated by a two-year-old' but I knew as soon as we left the room, they were hissing, 'Can you believe they don't put their child down for a nap? How irresponsible is that?'"

Food is also a sensitive issue. A writer on a website called Canadian Living outlines the risks. "My sons, who had only ever eaten soy hot dogs, got their first taste of the meat variety when the other mother loaded their sticks."

Lord alive, you pity those sinning meat-eaters, but her attitude is no worse than the sanctimoniousness I know I once felt in a Normandy supermarket, putting camembert in the trolley on top of a friend's Cheesestrings.

Clare Saunders, a full-time mother of four, says the only way to enjoy a shared holiday is to have shared expectations. "My most stressful holiday ever," she says, "was when some friends who had rented a villa in Italy were 'upgraded' at the last minute and asked us along to share the house. We felt obliged to them from the start. It was so much more expensive than anything we could have afforded and really my children were too young for that sort of a holiday. They are lovely people, but the pressure of keeping up with them was just awful. The house was amazing: gates and cypress trees.

"Caroline arrived with a spray-tan, and got less brown as the holiday progressed - she had all these amazing bikinis with matching sarongs and flip-flops - and her children were immaculate. I was pregnant and lumpy and exhausted.

"The big problem was that we had agreed to share the catering, one day on, one day off. When they were cooking, they would leave their children with their nanny and go off sourcing exquisite ingredients, salami with truffles, for example, driving miles to a town where they had read up about the olive oil. And you'd come down at dinner and the table would be laid, with flowers, a white tablecloth and they'd be showered and changed into lovely pressed clothes.

"But then, when it was our turn, we'd both be trying to do the children, it would be bath time and everyone would be screaming and whinging and we'd be hissing, 'Go and get the marinade on' or, 'For goodness' sake, start chopping'. It was like having a dinner party every single day. We were at each other's throats, but quietly so they wouldn't hear. Keeping up that level of appearance was exhausting.

"When we got home, everyone said, 'Was it a lovely holiday?' and I said yes. But it wasn't. It was a nightmare."

Parents with older offspring appear to have fewer cautionary tales. On the one hand, a holiday is less of a misnomer when the children can entertain themselves, and on the other they have learned what works and what doesn't.

Activity-based holidays seem generally to be a success - skiing, or water-sports, when you are entertained during the day and flop together at night. Also higher on the success stakes is any holiday where the cooking is taken care of. "Club together and get a cook if you can afford it," says Jones. "It saves everyone's sanity."

Half of the seasoned duo-vacationers I talked to told me it was important to put the children's friendships above the adults, and the other half said holidays were only a success if the adults got on. Both groups agreed, on the other hand, that too much proximity, even to people you love, can lead to lack of perspective. "You can share a holiday with other people without having to share everything about it," agrees Irvine. "If you want to go off and explore the local monastery, that's fine, but make sure you don't judge your friends for wanting to read GulfWeekly by the pool all day."

Sarah Mahoney, a district nurse, who has two children under 10, spent last summer with another family. "They had one of those great big Chelsea tractors (SUVs). And every morning, when we were setting off somewhere, they would say, 'Come in our car. We can all fit.' And I would be screaming internally, 'I don't want to go in your car, and have to leave when you want to, and do a little detour to the different beach you want to look at, or stop off for nappies.' This year, I will make sure I build into each day a little bit of time, with my family, on my own. It will make all the difference."

"Separate houses are good," says Helen Irvine. "Better still, separate continents." Irvine is one of the more vociferous opponents of shared holidays, so you can imagine she herself has learned to give them a wide berth. "Actually," she admits, "we go on holiday with the same family every August. Every September I say to everyone else I know, 'Shoot me if I say I'm going to do that again.' But, yes, we've just paid up again this year."

And why might that be? "The children, of course. The children always have a ball."

Incidentally, on the topic of that chocolate cake? I realised my error overnight, drove to the cold store in the early hours, bought a chocolate gateau and squished, filled and re-iced the sponge so brilliantly that nobody ever noticed.

(Some names have been changed)