Jemima Lewis: What my granny told me about class

So that's it, then: the classless society is upon us. A survey published this week claimed that the old social order is melting away, as Britain becomes one vast, amorphous middle class. The report, by the think-tank Future Foundation, found that in the past 40 years, the proportion of Britons who describe themselves as middle class has risen from 30 per cent to 43 per cent.

The working classes can still claim the majority (at 53 per cent) but not for much longer: by 2020, they will have been overtaken by the new bourgeoisie. The aristocracy is on the point of extinction already: only 1 per cent have the gumption to describe themselves as upper class.

At first glance, then, this looks like a vindication for John Major and Tony Blair and all the other politicians who have sought to level the social playing field. The rise in mass affluence, the increase in home ownership, and the expansion of higher education have helped to smash down the barriers, bringing us all together in one happy, homogenous, suburban melting pot.

A likely story. The human instinct for hierarchy is amazingly tenacious, and no one does it better, or with more fiendish subtlety, than the British. The authors of this survey were perplexed to discover, for instance, that people did not always rank themselves according to the size of their income or the grandeur of their profession. Thirty-six per cent of builders described themselves as middle class, while 29 per cent of bank managers insisted they were working class. The few who described themselves as upper class actually had lower incomes than the middle classes.

None of this should come as a surprise. The whole point about the British class system - the reason it continues to provoke such anger and fascination - is that it is complex almost beyond human endurance. Instead of being a simple ladder, with rich people at the top and poor at the bottom, it is a vast cobweb of gossamer-fine social distinctions - incomprehensible to the outsider, largely baffling even to us.

Most of what I know about class I learnt from my grandmother, who - though only a farmer's daughter - has a dowager duchess's nose for social nuance. She taught me all the things it was common to say - such as pardon and lounge and "ever so" - and then tested me on them, typing out exam papers with questions such as "What is the proper meaning of 'toilet'?" or "When should you use a doily?" (Answer: Never.)

A reluctant student in every other field, I loved my granny's lessons in snobbery. As a child of the 1970s, surrounded most of the time by non-judgemental progressive thinkers, I found it exhilarating to be with someone who firmly believed that you could, and should, judge a man by his shoes.

There was nothing underhand or snide about Granny's class- consciousness: on the contrary, she was always keen to rescue the common folk from their own errors of taste. People, she insisted, were "grateful to be told" if their curtains were an eyesore, or their sideburns made them look like a lorry driver.

I did not share her reformist zeal. For me, the pleasure was always in cracking the code: pinning down the myriad clues that distinguished, say, the upper-middle class intelligentsia from the middle-middle classes. I scrutinised my own family closely, trying to decide to which sub-strata of the bourgeoisie we belonged.

On the one hand, my parents earned a pittance. (At one point my father discovered that he could almost double his income if he became a bus driver.) On the other, they had distinguished-sounding jobs. (My mother worked for a literary agency; my father was a publisher turned author.) Our house had threadbare carpets, rotting woodwork, and dust and cat hair drifting across the draughty floorboards. Yet, confusingly, this was one of the posher things about us.

My friends at convent school, whose fathers were mostly policemen, plumbers and taxi drivers, lived in far greater comfort. They had white, deep-pile carpets and Jacuzzi baths. Their houses were toasty warm; the television was always on; there were Wagon Wheels and family-sized Coke bottles in the fridge. I envied them all this, at the same time as feeling uneasily superior to it. They, in turn, were shocked by my impecunious living arrangements - especially my mother's habit of serving lentils and brains for supper - but also unnerved. I sounded posh, yet I'd never even been on a foreign holiday. Were they missing something?

Of course they were: that's the whole point of having such a complicated class system. If it were just about money, any old arriviste or foreigner might muscle their way in at the top. The British upper classes - and later the upper middles - realised that fortunes come and go. To preserve their position in the hierarchy they had to invent a secret code: one so full of contradictions and surprises that only the most determined interloper could crack it. This is both the strength and the weakness of our class system: it's pervasive, pernicious and often unkind - but at least it's not driven by cash.