pete, you asked!: DD1 got 10 A's in one stitting at the end of Y11, DD2 got 11A's in one sitting at the end of Y10, DD3 got 11 A's in one sitting at the end of Y10, DS1 got 12 A's in on sitting at the end of Y10. No modules were taken, all linear. They are in good company at their school. None are at the top of their cohort in terms of achievement except arguably DS1 who at least shares that place with others. His 100% score in nine out of ten AS papers certainly managed to p*ss off his sisters, who regard him as a bit of a joke (he does it with no apparent effort; I think there is something wrong). DS1 is by no means complacent about getting a place, he knows there's far more to it than grades.
I think I read in the paper after last year's GCSE results that 23 pupils at South Hampstead High got 11A*s, though that's from memory.
You said a couple of days ago on another thread that your DS was at possibly the greatest school in the world and was a scholar there, so I'm surprised that you're surprised at results like these. I bet all the good London day schools and top grammars produce similar results year on year and I'd have thought your own DS's school would be bound to do so if it's world beating as you say.
Our HT said that 10/ 11 A*'s puts a student in the top 2%. I didn't say that the top 2% apply to medical school, I'm sure applicants are much more scattered across the spectrum than that. I would expect that most of those top 2% do apply to the top universities though, which is why I said they wouldn't regard those results as unusual, for them.
In the past four UCAS cycles a significant number of the DCs' friends have gone to medical schools with grades similar to this but also with lower grades. All pretty set on that career though, that I would say and clearly showed their aptitude at interview which your 12 A* student friend seems not to have done.