There are some very interesting and insightful posts on this thread.
As an Oxford admissions tutor, I have been very disheartened and angry even to read all the media articles about Oxford over the last couple of days. These articles just reinforce the notion that Oxford is an elitist place, where Northerners, BME students and students from state schools will not be made to feel at home. Nothing could be further from the truth!
No, the University admissions system is not perfect, but I and virtually all my colleagues in my subject are hyper-aware of the need for access and outreach, and extremely keen to admit BME students and students from the more under-represented regions of the UK. The pool of applicants varies from college to college and subject to subject, but in my subject, a majority of applicants are white and from independent schools in London and the Southeast. What the article provided by mateysmum states is very true: you can't admit people if they don't apply.
It is very frustrating to see how few state school students and Northerners apply, but even so, I admit every state school student I can. Many of these students end up with Firsts, and more than one has told me that they were advised by their school not to apply to Oxford because they were not good enough to get in. 
A few comments above that made me wince:
I think it's probably a mix of northerners not being so keen to go and Oxford not being so keen to take them.
Oxford is delighted to take northerners FFS! Remember that a fair number of tutors are northerners themselves. I cannot imagine any tutor thinking, 'Hmm, this applicant seems clever, but oh dear, they are from the north, I had better choose a southerner instead.'
'When Oxbridge say they want the academic best I do not beleive they allow for these differences in educational experience that patiently exist even between state schools let allone when you bring in private schools.' Yes, this. I think many of the people involved in admissions won't even be aware of those differences. Many of them will have children at state school themselves and think they understand the whole breadth of the system but they don't realise how atypical the good Oxford state schools are.
Admissions tutors ARE aware of the differences between state schools. Did you know that many of the state schools in Oxford are in fact historically NOT very good, because in Oxford many of the more privileged middle-class children go to independent schools rather than state? Outside Oxford, in the villages of Oxfordshire, there are many outstanding state schools, but historically the schools within Oxford itself have struggled with low results. My children go to state school, I am a school governor in addition to being an Oxford tutor, and I'm keenly aware of the stats. The Cherwell School, a state secondary in North Oxford, is rated outstanding, but houses in that catchment area easily cost a million pounds. The state secondary closest to where I live in Oxford recently went into special measures as a failing school.
deep breath
What I and my colleagues at Oxford would love to see would be students from every school in the UK applying here. Because every year, we get hundreds of applicants from places like Eton and Winchester, but there are dozens of secondary schools who have never helped one of their students apply to Oxbridge, ever. It is applicants from those schools we want to see!