If I owned a cap I would doff it today to the admissions director at Oxford University. He has just announced that students with top grades who live in the poorest areas and who have suffered a disadvantage such as being in care will now be guaranteed an interview and not turned away like mangy dogs. Hurrah! Let's have a celebratory food fight.

You'd have to be a special kind of dimwit not to see that an A grade achieved by a kid from a turd-strewn sink estate whose father drinks the housekeeping money before battering the mother is worth 20 of any A gained by a hothoused child in one of those ruthless exam-passing factories known as private schools.

It flags up far more thrilling potential than that of the state school pupil with the helicopter parents, Kumon maths lessons on tap and books in the house other than the one hidden in the kitchen drawer for the loan shark. Because, obviously, the deprived child has overcome every handicap by talent alone and thus is exceptional.

But, hark. Again we hear the familiar cry of “foul play” and “discrimination against the middle class” as Oxford tries to level a laughably uneven playing field. The high master of St Paul's, southwest London, reportedly thinks the postcode policy “deeply offensive” and patronising to young people, arguing that 18-year-olds should be “judged on their ability and not on their social background”. Eh? But people have been judged by their social backgrounds in this class-crippled country for centuries: if your daddy was a doctor you were “in”, if he was a docker you were “out”. Meanwhile, the director of the Centre for Education and Employment Research at Buckingham University says: “The Government is keen on social engineering and Oxford University seems to be bowing to that.” Hello? What are private schools if not academies of social engineering dressed up in a boater hat? What is moving house, faking religion and overtipping the church collection plate so that you can get into a prestigious faith school? Just social “finessing”?

It is interesting that a study last year found that sixth-formers were twice as likely to get into Oxford or Cambridge if they attended private schools regardless of their A-level results. Oxford admits only one in ten students from deprived areas, compared with almost a third at other universities.

You'll probably recall Middle England having a hilarious hissy fit a few years ago over Bristol University's decision to take applicants with lower A-level grades if they came from comprehensives. Cue the shrieking protests of the privileged few confronting the beastly possibility that, for once, every odd might not be stacked in their favour.

But Bristol had a point. Research has shown that students from the best schools and with the top grades don't necessarily go on to get the best degrees. A study of every graduate in the UK who left university in 1992-93 found that a male student who attended a private school was 6.5 per cent less likely to get a first or upper second than a student with the same A-level grades who attended a state school. The equivalent figure for females was 5.4 per cent. And get this: the higher the fees charged by the school, the less likely the student was to get a good degree compared with others who had the same pre-entry grades. How very cheering.

Private schools are adept at coaching pupils beyond their natural abilities. They deliver results, sometimes even for those who are quite thick. But this tells us little. Money can buy most things but not free thought, not authentic cleverness. Left to their own devices at university and divorced from intensive exam mentoring, a number of private pupils do not excel. Now there's speculation that wealthy parents will begin renting properties in scummy postcodes to massage the system - “Darling, it's time for us to visit the tenement again. Think of Oxford!” Quite possibly. There hasn't been a system invented that the pushy parent hasn't managed to circumnavigate.

This isn't a rail against private education: if that's how you want to lash £5,000 a term it's between you and your overdraft. What's offensive is the assumption that it should buy any sort of guarantee. If you bet on a horse you don't expect the system to ensure that you win, so why assume that a fortune spent in school fees should glad-hand you all the way to Oxbridge?

And anyway, Oxford isn't guaranteeing the deprived pupil a place, merely an interview. If they can tick three of five boxes: a poor postcode, time spent in care, attending a programme for disadvantaged children, and high performance at GCSE and A level then the applicant gets through to the next stage. Grades alone, they say, are too crude a measure and may overlook those children who break the mould. Now what, for pity's sake, is wrong with that?

Well, let's try to guess. Could it be that some parents fork out for private education because sink estate kids are precisely the types that they want to keep their precious progeny away from? Could it be that they're buying into a peer group that will smooth all the right introductions for the rest of their child's life, and now here come the oiks to bugger it all up?

Hell hath no fury like the privileged encountering a threat to their unchallenged march to the top. But why the insecurity, folks? Surely if your children are so bright they'll succeed anyway. Or might it be that you have so little confidence in their ability that you fear that without a gold-plated leg-up they'll end up in a call centre?

Leg-ups should work both ways. We are seeing in Beijing the results of a policy that says “if you're talented we'll invest in you whether you are from Eton or Brixton”. Many of those British medals (sorry, I can't use the term Team GB - it makes me nauseous) are down to Lottery money. Or those dirty words “public spending”.

Oxford, like other universities over recent years, is simply acknowledging the truth that some A grades are more meaningful than others. It's the intelligent decision. We'll find many more diamonds among the ugly tarmac of Britain's grimmest postcodes if we hold our noses, lift the lid and take the trouble to look.

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