gryffron wrote:PS. Do Oxbridge ...
Any monolithic question like that, the answer is No. Or, more accurately, N/A.
You don't apply to the University, you apply to one of the Colleges. Different colleges, and indeed those within them responsible for your subject, each take their own approaches.
If the college you apply to considers you a strong candidate but doesn't itself offer you a place, only then does your application get seen more widely when it gets put in "the pool" for consideration by other colleges whose policy extends to looking at such applications. That happened to me, and I was very happy with the college that picked me. Thirty years on, my nephew went to the same college that had put my application in the pool!
As for A-level results, they're hopelessly inadequate: if you're a remotely serious candidate, those top grades are far, far too trivial to distinguish the sheep from the goats. My Cambridge Entrance exam (1979) was, by contrast, a real challenge - and my nephew sat something similar despite those exams notionally being abolished!
I don't know where those "3 Ds" stories come from: we were faintly aware that Upper Class Twits must be somewhere (after all, we still have a Royal Family), but our paths never crossed. There was a genre of joke about them, and Cambridge had a degree called Land Economy widely seen as a joke - a qualification for a PG Wodehouse character to manage the ancestral Estates.