Very few universities still do in-person interviews because of that bias. Only Oxford and Cambridge require them. UCL and Imperial offer them optionally.

Some courses like Medicine do have interviews at institutions that usually don't interview.

“Only” the two most famous (and arguably best, in a number of fields) institutions. They set the tone.

They're certainly a good indicator that the class system is alive and well in the UK, but since the rest of the universities rely on the Highers/A-Level results without any interviews I'm not sure what you are implying by "set the tone"

And clearing - i.e. what happens to match people to the vacant spaces left by those who didn't make the offer target - is almost 100% interview based, usually by phone and on results day.