Snobbery may have claimed some political scalps, but it also enriches our literature

Without it, the English novel and huge amounts of domestic drama would more or less cease to exist

Heaven knows, we had a great many important matters with which to occupy ourselves last week, ranging from the immigration figures to tax-gathering beyond the Tweed, and yet a considerable swathe of the nation's opinion-formers seemed to be animated only by the vexed question of snobbery. The fallout from Emily Thornberry's career-retarding tweet of a flag-strewn house-front in the Rochester and Strood constituency continues to descend. David Mellor has chipped in with an Olympian reminder to an upstart taxi driver to know his place, while coming up on the rails behind them are Andrew Mitchell's embarrassments and an arresting-looking TV documentary on the editorial protocols of Tatler, a magazine whose very existence is predicated on the existence of rigorously enforced social distinctions. We are a nation of snobs, one or two of the stiffer commentators have deposed, and ought to be ashamed of ourselves.

All true, no doubt, and I am afraid that when I read the account of the rebuke administered by Mr Mellor to the cabbie who may or may not have taken the wrong route home from Buckingham Palace I nearly burst out laughing at the thought that anyone could be quite so de haut en bas. At the same time, modern denunciations of snobbishness nearly always seem to be undermined by a fatal lack of definition. Certainly class-consciousness has something to do with it, and so does the air of intellectual-cum-cultural superiority which half-a-dozen journalists claimed to detect in Ms Thornberry's tweet about the white van man of Kent. On the other hand, most social historians would probably maintain that true snobbery is a much more complex affair than a peer of the realm looking down on the gardener who weeds his lawn and that, properly investigated, it is able to illuminate vast areas of our national psyche.

But to begin at the beginning, what is a snob? William Makepeace Thackeray's definition, given in his great early-Victorian primer The Snobs of England: By One of Themselves (1846-47) is one "who meanly admires mean things". My own guess is that snobbishness involves judging a fellow human being by criteria that are, in the end, arbitrary, a series of yardsticks that can equally well involve despising someone for having too much money rather than too little. Naturally, social class is one of the great snob dynamics. One reads some of the great snob diarists – Harold Nicolson, say, or James Lees-Milne – with a kind of incredulity at the fact that these paragons are selecting their friends on the basis of where they went to school, or the particular accident of birth that presented them with a title.

Lees-Milne, for example, was an exceptionally intelligent man, whose comments on the people he comes across are generally models of shrewdness, and yet he genuinely did believe that a compliment which came to him from a duke was worth more than one from a commoner and that his great chum the Duke of Devonshire was cut from a superior cloth to most of the acolytes who gathered around him in the Chatsworth drawing room. There is a rather defiant moment in one of his late-period chronicles when he asks himself why he so much admires the duke's wife, Deborah. "Because she is a duchess? Largely, yes …" But strawberry leaves, you see, have brought out qualities she already possessed, and "in any crisis she would come out on top".

Most of us born beyond the purple would probably read this with the same bewilderment that we bring to David Mellor's strictures on his cabbie, for it is so obviously beyond reason – on the same level as a belief that the Earth is flat or that the aliens landed centuries ago and infiltrate our counsels as we speak. And yet a glance around society as a whole demonstrates how pervasive is the judgement built on a false standard and that it extends to practically every area of human interaction. The Snobs of England, for example, insists that there are snobs "everywhere, in all companies, from morning to night, from youth to the grave", and offers such categories as "country snobs", "clerical snobs" and "English snobs on the continent". My father used to maintain that the part of the council estate on which he lived in the 1930s was an absolute hotbed of snobbery, consisting as it did of 16 families, some of whom considered themselves "respectable", others of whom fought in the street on Saturday nights, and all of whom were avid to acquire a "double-bay front", that is a superior dwelling with two bay windows.

So to be a snob is to look down on your fellow citizen for reasons that have nothing to do with his or her innate worth or merit but are bound up in symbol, usage and instinct. The channels through which snobbery is carried, consequently, are rarely to do with obvious things – the big house, the full wallet – but connect themselves up to tiny gestures or infinitesimal behavioural tics: knowing what a gerund is, being able to recognise the Merchant Taylors' Old Boys' tie, accurately pronouncing someone's name. "Ivy Compton-Burnett we call it" Anthony Powell once corrected my attempt on that distinguished lady novelist's moniker, which was not an example of Powell being snobbish himself but remembering her put-down of his own rendition when they were first introduced. And Ms Compton-Burnett, just to reinforce the point, is generally reckoned to have come from the prosperous middle classes.

All of which may perhaps serve to reinforce a suggestion that the keenest snobs (pace Ms Thornberry and Mr Mellor) are not those stratospherically removed from the majority of their fellow citizens by dint of intellect or social position but those divided from them by the width of a garden fence. A marquis never thinks of patronising a postman: what is the point? On the other hand, the family that glories in the fact that it has managed to procure a slightly more expensive car than the one next door, or whose son accumulates 10 GCSEs at grade A when the half-wit over the road secures only seven are true snobs, of whom Thackeray would have been proud.

But if snobbery relies on the ramming home of a marginal advantage, then at the same time it can also flourish in conditions where advantage is, or was, so profoundly lacking as to become a point in your favour, finding its roots in poverty or regional affiliation or accent or a combination of all three.

Dennis Skinner, for instance, is quite as much of a snob in his way as James Lees-Milne, and so are Monty Python's four Yorkshiremen, and so is Geoffrey Boycott. I myself am the kind of snob who goes through the sports reports in the local newspaper with a felt-tip pen putting exclamation marks next to the mixed metaphors and the split infinitives.

Left-leaning social critics occasionally complain about this element of British life without realising its fundamental importance both for the individual's sense of his, or her, identity or the consequences for art were it to be taken away. For without this attention to minute social and intellectual gradations, the English novel and huge amounts of domestic drama would more or less cease to exist. No Thackeray, no Charles Dickens, no Kingsley Amis, no Virginia Woolf (who has some claims to be one of the most snobbish women ever to put pen to paper). Somehow it seems a small price to pay for the Mellor meltdown and Andrew Mitchell's vain attempt to impose his personality on the minions of the Downing Street gate.