Strange as it might seem, we owe some thanks to Digby Jones - because he has reminded us that social mobility is a con.

Over the weekend he tweeted:

Enough! I can't stand it anymore! Alex Scott spoils a good presentational job on the BBC Olympics Team with her very noticeable inability to pronounce her 'g's at the end of a word. Competitors are NOT taking part, Alex, in the fencin, rowin, boxin, kayakin, weightliftin & swimmin.

Now, Ms Scott epitomizes the meritocratic ideal of someone coming from a poor background and succeeding through personal ability. She is a child of Thatcher:

it doesn't matter what your background is. I believe in merit, I belong to meritocracy, and I don't care two hoots what your background is. What I am concerned with is whatever your background, you have a chance to climb to the top.

Jones by contrast is telling us that background does matter. However brilliant a working class person might be, he will find a way of hating them.

Of course, not all of those in the establishment blurt out their hatred as crassly as Jones did. Just as many racists avoid using the N-word, so class haters are rarely so explicit. Nevertheless, his attitude is widespread. Here for example is Sajid Javid:

He describes going for an early interview at Rothschild and being confronted by a row of white men in pin-striped suits who asked him what his father did and where he went to school. "The British merchant banks in those days would always go to the old school tie. If you didn't go to the right country parties and spend the weekends in the right place you had got no connection," he says. "I thought even if they offer me a job I'm never going to fit in."

Everybody of obviously working class origin has experienced a degree of froideur in our encounters with posher colleagues, clients or bosses. With better men than Jones - and you can carve a better man than him from a turd - this will be subtle: those Rothschilds men were no doubt impeccably charming. But there is always a sense of being othered, a mutual awareness of difference - which, if you point it out, invites the accusation of chippiness. There is always, always, an undertow.

The best relationship the upwardly mobile can expect with posher colleagues is that of a trusted NCO with a good commissioned officer: it might be friendly and effective, but both sides always know there's a difference.

One effect of all this is to depress social mobility. Sure, some people like Javid and myself can find well-paid jobs outside Rothschilds. But there are fewer places for us than there are for the posh boy.

And this can happen without overt class hatred of the sort displayed by Jones. It's wholly reasonable for employers to want people they can trust or who look like they are safer bets. Like hires like - which diminishes the chances of people from working class backgrounds, or women, or ethnic minorities, or the disabled.

And those who overcome these barriers face another problem. We can never fully transcend the class of our birth. People from working-class backgrounds earn less than those from posh ones even when they have the same levels of experience and education. That's because networks operate to their disadvantage.

Such networks diminish social opportunities as well as career ones. Men from poor homes are less likely to be married in later life (pdf), even controlling for their own incomes. This isolation, allied to the subtle stresses of living a life in unfamiliar surroundings is bad for our heath. As Michael Marmot has written:

Where you come from does matter for your health...Family background, measured as parents' education and father's social class, are related to risk of heart disease.

We know that immigrants tend to suffer from worse mental health than others. Perhaps migration across class borders has a similar effect.

All of which makes me think that Adam Smith had a point:

The poor man's son, whom heaven in its anger has visited with ambition...labours night and day to acquire talents superior to all his competitors. He endeavours next to bring those talents into public view, and with equal assiduity solicits every opportunity of employment. For this purpose he makes his court to all mankind; he serves those whom he hates, and is obsequious to those whom he despises. Through the whole of his life he pursues the idea of a certain artificial and elegant repose which he may never arrive at, for which he sacrifices a real tranquillity that is at all times in his power, and which, if in the extremity of old age he should at last attain to it, he will find to be in no respect preferable to that humble security and contentment which he had abandoned for it. It is then, in the last dregs of life, his body wasted with toil and diseases, his mind galled and ruffled by the memory of a thousand injuries and disappointments which he imagines he has met with from the injustice of his enemies, or from the perfidy and ingratitude of his friends, that he begins at last to find that wealth and greatness are mere trinkets of frivolous utility.

The point of all this is not to say that young working class people should not be ambitious. Instead, it is to suggest that social mobility is no substitute for genuine equality.