To my mind, the silliest headline of the 2000s appeared in the Times of 5 May 2006. Some academic had decided that what job you had, how much money you earned and who your parents were did not matter a damn in go-ahead Britain. Snobbery was dead. Meritocracy was here to stay. The Times ran this welcome news under the title: "We are all middle class now as social barriers fall away." No one will take this nonsense seriously, I thought as I tossed the paper aside. But I reckoned without David Cameron.

Trying to soften up parents for cuts in the Sure Start programme, he said that as soon as a new centre opened the "sharp-elbowed middle classes – like my wife and me – get in there and get all the services". Note the dexterity of his manoeuvre. He and Mrs Cameron knew how to play the system, he confessed. But what set them apart from the rest of the grasping middle class was that they were honest enough to admit their faults and honourable enough to want to help those less fortunate than themselves, even if he did say so himself. He would renounce greed in an act of Christian contrition. He would put the interests of the poor before the interests of his own class. And hope, while onlookers applauded his altruism, that they would not notice that the aim of the exercise was to remove services for young mothers.

Everything was wrong about his speech, and not even wrong in an original manner. Cameron was continuing the ridiculous tradition of establishment types slumming it. For a half a century, the British elite has pretended that it does not exist. "The class war is obsolete," Harold Macmillan declared after winning the 1959 general election and then promptly formed a government which included a duke, three earls and a marquess. "I want to take class out of British politics," said Tony Blair and then presided over the largest bubble in capitalist history and an orgy of conspicuous consumption.

The Camerons' belief that they are middle class, when he is the son of a stockbroker and she is the daughter of a baronet, shows that they, too, possess the least attractive characteristic of the men (and occasional woman) at the top of the hierarchy. They cannot admit that they are privileged.

The rightwing press inadvertently produces evidence of the scale and persistence of the delusion. When the old Labour government considered removing charitable status from private schools, it described the proposal "as an attack on the middle class". Parents, who send their children private, need to find a minimum of £10,000 per child per year after tax. Those who can afford to do it are, by any reasonable standards, wealthy. The same papers also denounced Labour's decision to raise the top rate of income to tax to 50% on salaries over £150,000 as another blow to long-suffering middle England. They did not seem to know that an income of £150,000 puts you in the top 1% of earners.

If middle class means being in middle of society, then the median wage in Britain in 2009 was £21,320. Admittedly, most households have two incomes. Even then, the Department for Work and Pensions says that the average household income for a couple with no children is the less than princely sum of £407 a week after tax. The typical middle-class Briton is not a doctor or barrister but a clerk or shop manager. They do not put their children's names down for Eton or worry about the 50% tax.

Sociologists become agitated when you define class by wealth. The university graduate, who listens to Radio 4 but cannot and will not ever land a well-paid job, is clearly not culturally a part of the working class. Equally, the leftish artists and politicians who insist that they are working class even though they were born into professional families and make a good living, do not share the same culture as solicitors from the home counties. The researcher the Times was praising claimed that the only way to tell classes apart was that the middle class deferred gratification and saved, while the feckless working class spent like there was no tomorrow.

For all these caveats, money defines you in the end. If you live a life of shabby gentility for too long, the shabbiness overwhelms gentility and your downward mobility becomes permanent. The best writers in English literature – and what other literature in the world can boast such a minute and merciless examination of social status? – have always known the importance of money. As WH Auden said, only half-jokingly, of Jane Austen:

You could not shock her more than she shocks me;

Besides her Joyce seems innocent as grass.

It makes me uncomfortable to see

An English spinster of the middle class

Describe the amorous effects of "brass",

Reveal so frankly and with such sobriety

The economic basis of society.

Where this government of wealthy men is already going wrong is that, unlike Austen and Auden, it misunderstands the economic basis of society.

Living in London and moving in a social world dominated by the huge salaries from the City, ministers overestimate the wealth of middling people. They will cut their benefits and services, raise their taxes and denounce their sharp elbows because they think that the British middle class is composed of men and women like them.

They ought to be careful. Apart from money, one other feature defines the middle class. It has a well-merited suspicion that vested interests based in London will do it down.

I once tried to compile a list of all the scornful phrases the British use to warn politicians, BBC executives, bureaucrats, bankers, speculators, benefit scroungers and everyone else who wants their money not to go too far. "Who do you think you're talking to?"; "Who do you think you are?"; "Do you think there's one rule for you and one for the rest of us?"; "Do you think you're above the law?"; "You're trying it on/taking a liberty/taking advantage/taking the mickey/taking the piss."

If David Cameron continues to treat mothers whose lives he does not begin to comprehend as sharp-elbowed hustlers, he will soon find them elbowing him where it hurts.