What do you want to be when you grow up? I remember a careers advisor asking me just that question shortly before my sixteenth birthday. Like most of my peers I had very little idea as to what I wanted to do with my life when the seemingly endless horizon of school came to an end. Drink beer, smoke cigarettes and chase girls was about the sum of it.

Looking back, though, the question was a strange one. We insist on asking children what they want to do with their lives when most of the time it’s set in stone when they pull on their first school uniform. If they are born poor they will almost certainly stay poor; if their parents have money then it’s likely that they will too. The more unequal a society is the truer this statement becomes.

Yes we insist on telling children that they can be ‘whatever they want to be’, knowing full well that crushing disappointment lies further in their future. Every nation relies to some extent on fairy tales. In Britain we cling to the idea that you can be or do anything in life so long as you put your mind to it. In the process we hand our politicians the one thing they can use to justify the obscene privileges at the top and the revolting squalor at the bottom: the indomitable myth of meritocracy.

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Meritocracy is what’s politely called a dead duck. A child from a ‘modest’ background can only go from rags to riches in the sense that a human being can take off if they flap their arms around wildly enough. A disadvantaged child will nearly always and everywhere become a disadvantaged adult, and if you ignore the right-wing rhetoric and look at the data you might be a little less keen on hearing the 'M' word in future.

The children of wealthier parents are more likely to go to the best schools (houses in desirable catchment areas cost on average 42 per cent more), eat the best food, have access to ‘high culture’ and have a quiet place to do homework when they get home from school. As a result, poor but bright children get overtaken by their less intelligent classmates from wealthier backgrounds in the very first years of schooling, according to a 2007 study.

As children become teenagers these inequalities are entrenched further. Around 10 per cent of young people at the bottom rung of the social ladder go to university compared with over 80 per cent of those from professional or managerial backgrounds. A student from a private school is 55 times more likely to go to Oxford or Cambridge University than a state school student on free school meals. And as universities minister David Willetts likes to point out, graduates will earn around £100,000 more over a lifetime than non-graduates.

Thomas Piketty’s ground-breaking book Capital in the 21st Century looks at how wealth concentrates when the returns on capital are higher than economic growth. Or in plain English, how it’s easier for a person who already has lots of money to make more of it. But it isn’t only wealth that concentrates; opportunity does too. Or as Picketty’s predecessor Karl Marx put it, “men make their own history, but they do not make it as they please; they make it…under circumstances…given and transmitted from the past”.

Take a look at political life in Britain today and the truth of that statement becomes self-evident. When Margaret Thatcher came to power in 1979 around 40 per cent of Labour MPs had done some form of manual or clerical work before they entered parliament. By 2010 that figure had plummeted to just 9 per cent. The shape of the labour market undoubtedly accounts for some of the change, but the extent to which parliament is rapidly becoming the talking shop of the middle classes is evident in other ways too. An astonishing 91 per cent of the 2010 intake of MPs were university graduates and 35 per cent were privately-educated. This is a rise on previous elections and, in the case of the latter, compares to just 7 per cent of the school age population as a whole.

If nothing else, the fact that a tweed-suited former stockbroker can pose as just an ordinary bloke when contrasted with other politicians should set the alarm bells ringing. The ossification of politics is made worse by a media which increasingly resembles the establishment talking to itself.

The unpalatable truth that no politician will dare acknowledge is this: meritocracy can only exist if the rich have a little less and the poor a little more. Countless studies show that social mobility improves in more equal societies. Norway has the greatest level of social mobility, followed by Denmark, Sweden and Finland. Britain and the US are the most unequal western societies on earth in terms of income distribution and, surprise surprise, have much lower rates of social mobility than their more equal Scandinavian counterparts.

Despite the well-intentioned rhetoric of Ed Miliband, we are not ‘one nation’, and the first step in creating a genuine meritocracy would be an admission that the interests of the banker are not the same as those of the nurse or the refuse collector. While huge inequalities exist there can be no serious talk of social mobility or meritocracy, and careers advisors up and down the country will have to keep on lying to our children.