On Radio 4's Media Show yesterday Andrea Catherwood told Sarah Sands, the incoming editor of the Today programme:

The job specification did say that there was a requirement of extensive experience of broadcast journalism and a sound appreciation of studio broadcast techniques. You obviously got over that hurdle (16'23" in).

Many of us, though, wouldn't even have tried the hurdle. If I'd had Ms Sands otherwise decent CV, I'd have looked at that job spec and ruled myself out as unqualified. Ms Sands, obviously, did not.

In this, she's following many others. Tristram Hunt has become head of the V&A despite no experience of curating or of running large organizations. David Cameron wanted to become PM because he thought he'd be "rather good" at it - a judgment which now looks dubious. And the last Labour government asked David Freud to review welfare policy even though, by his own admission, he "didn't know anything about welfare at all."

These people have something in common: they come from families sufficiently rich to afford private schooling*. And they are not isolated instances. The Sutton Trust has repeatedly shown that people from posh backgrounds are over-represented in top professions. This is unlikely to be due solely to superior ability; people from working class backgrounds earn less than those from professional backgrounds, even controlling for qualifications and experience.

One thing that's going on here is a difference in confidence. Coming from a posh family emboldens many people to think they can do jobs even if they lack requisite qualifications. By contrast, others get the confidence knocked out of them (16'20 in)**. As Toby Morris has brilliantly shown, apparently small differences in upbringing can over the years translate into differences not only in achievement but also in senses of entitlement.

The point is not (just) that people from working-class backgrounds suffer outright discrimination. It's that they put themselves forward less than others, and so save hirers the bother of discriminating against them.

But why do posh people get the jobs for which they're unqualified? One reason lies in experiments by Cameron Anderson and Sebastien Brion. They've shown than people mistake confidence for actual ability, and so tend to hire the irrationally overconfident - even to the point of hiring dangerous narcissists (pdf).

A further reason is that like hires like. In part, this is because a reasonable motive has a less reasonably effect. People need to trust those they hire - especially if they are in important jobs - and we naturally tend to trust people like ourselves. What's more, the privately educated have smooth manners and social "skills" and so fit in. "In the drawing-rooms of the great" wrote Adam Smith, "the abilities to please are more regarded than the abilities to serve."

Herein lies an issue. In hiring Ms Sands (and no doubt many others like her) the BBC is conforming to a pattern whereby inequality perpetuates itself. This suggests that the corporation is badly placed to address what is for many of us one of the great issues of our time - the many aspects of class inequality - because it is part of the problem. And it compounds this bias by focusing upon other matters instead - for example by the incessant airtime it gives to the (Dulwich College-educated) Farage***. Bias consists not merely in what is said and reported, but in what is not - in the choice of agenda. In matters of class, the BBC is not impartial.

* This habit isn't confined to the UK. At least one American has recently taken a top job despite having neither requisite experience nor psychological qualities.

** I'm one of those. People have often told me I should have worked in academia or on a national newspaper, but I genuinely believe I am wholly unqualified to do so, and regard myself as borderline unemployable.

*** It is odd, is it not, that people from rich families think they can become the voice of the people and are presented as outsiders challenging the establishment.