Kate Saunders: Yes, I am a single mother...

If marriage is so brilliant, why do so many of us go to the trouble and expense of divorce?

According to the latest Social Trends report, just issued by the Office for National Statistics, 24 per cent of children are now growing up in one-parent families. Many newspapers helpfully pointed out that this was nearly a quarter of all families. The only surprising thing about it was that anyone was surprised.

I am a single mother, with a 14-year-old son. One of my sisters is a single mother with two daughters. We are both chronically short of cash, because it takes two incomes to run a middle-class life these days. We are often made to feel like poor relations - little Match-girls, staring through the lighted window at the happy nuclear families - but we can hardly say we're in a minority any more.

Twenty-four percent is too big to count as a minority. Generalisations about single mums will have to be adjusted - that's nearly a quarter of all mothers of school-age children, and we can't all have got ourselves knocked up on purpose to make the council give us flats. There aren't that many council flats in the whole world, and I hasten to add that far too many single mothers are still living in conditions of disgusting squalor.

Single mums, whether you like it or not, have become normal mums. And there are more of us marching over the brow of the hill. Forty-three per cent of babies are born out of wedlock these days, and one third of those parental units is likely to split up over the next few years - always assuming there were two parents in the first place.

The tectonic plates of the family have shifted. I would never have chosen to be a single mother, but plenty of women do. Why not, when they can see us 24 percenters somehow making a go of it? Only a couple of generations ago, women who got pregnant outside marriage were packed off to the nuns to hide their "shame". Nowadays, a girl doesn't need a permanent man to get herself what a girl really wants, which is basically babies (please don't argue - I dare say there's a statistic for this too, but I can't be bothered to dig for it). A father is becoming a less essential part of the modern household.

Marriage has become biodegradable. Relationships come with sell-by dates. We are now a nation of serial monogamists, who expect to fall in love more than once. A dog licks its balls because it can, and modern men often seem to bugger off for the same reason - but don't imagine I'm blaming the new, fractured family on men. It's not as simple as that.

As the mother of a son, my heart rather bleeds for the male sex at the moment. Imagine what it must be like, when every girl you meet expects you to give her a house and support her while she indulges her hormonal urges - one brief snog, and suddenly you're lumbered with the Madonna of the Rocks. No wonder they make for the hills. I'm already telling my boy how to spot a sperm-bandit.

Unfortunately, impressionable young women are still being bombarded with images of the supposedly perfect traditional family - in every advertisement, for instance, which is always a reliable indicator of the way we wish we were. All-butter shortbread is no longer made by ladies in muslin aprons, and the average woman can no longer assume some poor man will pay her way through a luxurious career of stay-at-home mothering.

These days, only the very rich can afford to bring up their own children (the very poor do not have a choice in the matter). This is silly and depressing, but it's one of those sour little facts that won't go away. We're chasing an ideal that has already passed into history, like coal mines and steam engines. Yes, it's rather sad - in my childhood, more men earned enough to feed, clothe and house a wife and her brood, and from the child's point of view, it was bliss.

Don't let's forget, however, that this paradise had its fair share of serpents. If the traditional family is such a wonderful model, why are fewer of us choosing to stay in one? If marriage is so brilliant, why do so many of us go to the trouble and expense of divorce?

People split up these days because they can. That doesn't mean the process has become more fun. It actually means that before divorce was widely available, a very high percentage of marriages were miserable. So in the good old days, when father went to work and mother stayed at home with the mangle, 24 per cent of children were living in miserable homes.

The 24 per cent of single-parent establishments ought to amount to a strong political force. Politicians should pay some attention to these shiny new statistics, and stop assuming they are speaking to everyone when they bang on about Family Values. The family has taken on a different shape - many different shapes. And what the new family needs is more acknowledgement, more help, more state-funded childcare.

My sister and I are among the more fortunate single mothers, who can afford to pay nurseries and nannies, childminders and au pairs. Thousands, millions more are trapped in permanent poverty and isolation - and all because so few people are prepared to admit that they really exist in significant numbers. We do exist. Get over it.