I have two young friends at Oxford. They are brothers, and their sister also went there.
From my old comp, right here in County Durham.
That is not untypical.
In fact, I believe that it is correct to say that my old comp has sent someone to Oxbridge every year since it was founded, which was in 1966.
Again, that seems to be quite normal.
I am going through the 11-18 comps in County Durham, and they all send people to Oxbridge routinely.
Sixth Form colleges, I honestly know less about. But I could find out.
You could admit the entire Upper Sixth of every grammar school in the country, but you would come nowhere close to the 50 per cent of Oxbridge's annual intake that came from state schools.
That that is where they mostly come from is what the uncouth youth might call a "meme".
The rest of us can think of other words for it.