"What are we doing wrong?" Anya's mother Catherine - my best friend - asked despairingly as she wrestled her child to the ground. "Why do English children all behave this way?"

It was a rhetorical question. Catherine knows the answer. Ever since she married a Russian man and her brother married a Thai woman, and they all had children, she's been developing a fascinating grand theory about how national characteristics develop. If anyone would know why an English child acted English, it's her.

Many British people think it's not very PC to believe in national characteristics at all. It's considered vaguely Nazi to believe in any collective folk identity traced back to a gene pool. Even so, we secretly know that non-Brits see us (if not as public-school introverts, coldblooded and uptight, or as football yobs, male, drunk and aggressive) as individualistic to the point of eccentricity.

Still, Catherine's theory shouldn't offend, because she holds that national characteristics come from nurture, not nature. She believes that very young children learn to be English, or Russian, or Thai, at the same time as they learn the finer points of eating and potty training - and actually as a result of the training they are given in those basic human skills.

Here are her two examples.

Anyone who has been to South-East Asia will have been charmed by the way every Thai reverently steeples their hands together and bows his head as he speaks to you. But it took a Christmas of unfavourable family comparisons between Anya's English tantrums and the dignified charm of her Thai cousin - also four - for a red-faced Catherine to investigate how doing wai begins.

At the time of breast-feeding, it turns out. A Thai child who won't put a pair of tiny hands together and bob a tiny head doesn't get the breast. Imagine how powerfully that teaching must be implanted If your conditioning goes that far back beyond your power of speech, you and everyone like you can hardly help but turn out deferential, eager to please and highly socialised at an early age.

But think again before you start pressing your newborn baby's hands together and encouraging him or her to bob his head at you. There's a downside. As Catherine is also grimly fond of pointing out, the carrot-and-stick breast-feeding-and-waiing training may also explain the South-East Asian phenomemon of "running amok" - the moment of madness in those warm nations of gentle, low-voiced people, when, just occasionally, someone completely, wordlessly flips and goes wild with an axe. What else can they do? If obedience is learned at the breast, then any rare disobedience can only be expressed as complete disengagement from adult reality - a chaotic return to a pre-verbal time of primal screams and all-consuming rage. (Perhaps, Catherine concludes hopefully, an English tantrum or two is a lesser evil?)

Another family holiday - this time with the Russian cousins, surrounded by angelic little blondes with long plaits and giant bows and woolly tights that bag around the ankle, who also never have tantrums - gives Catherine another element to her theory. I always fancied the idea that Russian babies have their characters shaped by being swaddled in so many layers of clothes they can hardly move, and then put out on to the balcony even on the coldest winter night to give them fresh snowy air. But Catherine's theory is more radical (and just possibly influenced by her Russian mother-in-law's pointed comments about Anya's manners). Catherine says a Russian becomes a Russian during potty training.

British babies are, by and large, left in nappies until their muscles are developed enough to give them a fighting chance of getting to the loo on time - which happens at some time after they turn two. But Russian babies start "potty training" at nine months. Long before they gain physiological control over their sphincter muscles, their nappies are removed. From this moment on, they become completely reliant on the adult holding the potty to save them from embarrassment and humiliation that they can't control. Hey presto: Big Brother - as you grow up, your childish dependence on your family adults translates into a lifelong dependency on authority, in the form of an often arbitrary and tricky State. (Oh, and a tendency to sink into abject self-loathing and alcohol/fag abuse or worse to escape from the pressure of events you can't realistically hope to shape).

British children, by contrast , get left to themselves much more. While we as a society are probably blissfully unaware of all kinds of other odd things we make our children do, which must affect their personalities, I like the idea that they are likely to have a stronger sense of self as a result of not being forced to do those particular cultural things.

But I'd say the answer to the exasperated question Catherine started off by asking - "why do all English children behave like this?" - was simpler than she likes to think. It has as much to do with the delinquent learned behaviour of mothers as with the cultural programming of their children. If you want your babies to play nicely, smile sweetly, and share their toys with their siblings - whatever their nationality or personality type - just remember this. Never take them to Oxford Street on a Saturday afternoon.

Slices of London: e-mail Urban Fox here