Oh yes, completely forgot you can’t apply to both! (In the same year 😉)
It depends on what kind of extracurriculars. Obviously not the normal ones like being in the school clubs etc.
More along the lines of if the applicant has published a book, participated in public life at a high level (eg Greta T), started a movement of national significance.
There’s lots of A* kids out there, how do you tell them apart?
Obviously I’m talking from more than a decade ago, but from my friends and acquaintances the ones that got interviews/ places, one placed top 3 in a global subject Olympiad, one was a public speaker of significance aged 17-18 with a wide range of extracurriculars where she was a high performer, one was an international athlete in a sport that’s quite Oxbridge with an unusual family background, and one had written a book. Others that I know that applied with top grades didn’t get selected.
I do assume normal high performing kids get in but if you have a profile, in my experience that really helps your chances.
Again, that’s my experience and more in humanities than STEM. Perhaps STEM is more based on tests.
Maybe things have changed changed but as a student I used to work a part-time job for a highly sought after course where you needed the maximum grades to be considered (not Oxbridge), doing things like outreach etc. Every applicant had the same grade profile, so to be truthful almost all places went to people who were high achievers in the field beyond having a good A-level grade. The ‘normal’ kids who were just very good students stood out once the students started socialising and finding out about each other.