The basis of the article @dylexicdementor11 linked to use incorrect. At 6th form level, it’s not 6% educated in the private sector, it’s 17%.
The Cambridge stats are very transparent. The offer ratios made to those from different types of schools - independent, grammar, comprehensive, sixth form college and FE college are pretty much the same - if anything, the most favourable offer rates are for grammars and the lowest for FE colleges, but the differences are negligible.
17% of A-level students are educated in the private sector but they account for 24% of A star grades - which is what you need to apply. It stands to reason that private school will always punch above their weight in terms of A star grades simply because more of them are academically selective. You can’t compare a super-selective independent school like Westminster to a comprehensive - everyone at Westminster or similar schools will achieve the required grades for Oxbridge so it stands to reason more will apply. This is also true for very selective grammars.
On average nowadays, about 25% of A star grades are gained in the independent sector and this is reflected in the current state / independent offer ratio at Oxbridge.
The stats show that around 75% of Oxbridge entrants come from the ‘state sector’ - but this is misleading, because if you delve deeper into the stats, you will see that a very high proportion of these come from grammars or particular sixth form colleges such as Hills Rd in Cambridge or Brampton Manor in East London.
Just like a large proportion of the independent school intake is coming from the London super-selective day schools.
Cambridge have announced they are going to get rid of the state v independent criteria in their future admissions stats publications. This is because they have found that the ‘state demographic’ actually getting in is the same as the independent - ie. families in Bucks or Kent or North London who happen to be in grammar areas are no different to those in non-grammar areas who use independent schools.
So going forward, they will be tracking POLAR and ACORN stats only, as categorising by school sector has priced to be a largely blunt instrument in WP.