Jayne Dowle: It's not just the Duchess... we all live in a society that can't stop spending

But like 700,000 people in Britain, she has seen her fortunes wiped out in recent years. New research by Datamonitor has discovered that the number of "affluent people" has dropped dramatically since the recession took hold.

Before the credit crunch struck in 2007, nearly eight million Britons were classed as "affluent". This means that they had at least 30,000 in liquid assets, such as cash, savings, bonds and stock market investments. Property and pensions don't count. So if you can still lay your hands on 30,000, consider yourself very lucky indeed.

How do we measure affluence in real terms? One individual's definition of affluence might be another's poverty line. For millions of people, having 3,000 in the bank, let alone 30,000, would mean financial security beyond their wildest dreams.

For others, and I'm thinking of the bankers still raking in their mega-bonuses here, 30,000 would be a drop in the ocean on which their yachts will be cruising.

Affluence, according to one friend, means that you never need to use your credit card, an interesting observation considering our rampantly consumerist society has been built on the unblinking acceptance of debt. Personally, I would consider myself affluent if I could afford to do all my food shopping in Marks & Spencer and choose the most expensive face creams without looking at the prices. Shallow isn't it? But then affluence is. It's not about being able to buy what you need, but what you want. And it soon runs out of control. I know of one family who stretched themselves to the limit buying a huge house, and proceeded to deck it out with every gadget and technical gizmo known to man. Everybody thought they were doing well, enjoying their "affluence", throwing parties and so on.

One lad who went for a visit came back wide-eyed: "They've got a television in every room". Now I hear that their business has failed, and they have gone bankrupt. The bailiffs are at the door, demanding all those televisions back. I feel really sorry for their children, who are about the same age as mine. What awful formative memories this must be creating. Dad tearing his hair out, mum sobbing, a family home stripped of all its possessions.

This is the message I try to get across to my own son and daughter, without frightening the life out of them. Don't take anything for granted, and you can't have everything you want. Even Lizzie, who is only four, recognises that the extra hours mummy and daddy put in at work equals hard cash for new shoes and holidays. It is never too early to teach them about the value of money. And I don't just mean doling out the pocket money and leaving them to spend it how they like.

On holiday in Spain last week, I decided it was time to teach Jack, recently turned eight, to shop thriftily. We must have looked in every shop in Salou checking out the prices of knock-off football shirts, working out the best deals, before I allowed him to part with his birthday money.

He was hot and bored at first, but he soon got into haggling. And it did his powers of mental arithmetic a world of good. I don't want him growing up thinking that he can walk into any store, hand over his plastic and simply walk out with the goods without understanding how much they really cost – or how much he would have left in his account.

He is old enough to recognise the difference between having money and not. On his birthday, he asked me if we were "rich" because we could afford to give him a modest party. Already, he is placing his own family on a scale, comparable to his friends. So I think that understanding how affluent you are can't really be measured in figures alone. It is about accepting what your own personal limits are.

Everybody wants to get on in life, sure. But too many people believed that the only way to prove how far they had come was to spend, spend, spend on the trappings. Their own understanding of personal affluence was skewed by the easy availability of credit, the growing equity in their homes and the eternal desire to show off their "wealth" to everybody else in their orbit. My father still calls them "10-bob millionaires". In his day, they wore sheepskin coats, drove Jags and generally, were flash and lived beyond their means.

Every town and village had its share. But the problem is, we've ended up with a country full of them. A television in every

room and nothing in the bank.

If that's what affluence really means, then I'd rather keep counting the pennies.