palis the original point was about numbers. That fewer apply. That Classics therefore looks less competitive than say E&M or PPE or History but isn't when you scratch the surface.
Sorry to state the very obvious but numbers attending independent schools are a tenth or less of those attending school in the maintained sector. There's your main filter. All those kids will be able to access English and History; only that much smaller proportion will be able to access Classics. The option to apply for Course II is there, but is one of the toughest courses in the university, according to the tutors, both in terms of the fairly polymath(ematical?) skills required, also in terms of workload. So there just won't be herds of applicants rushing to break down the door.
The same can be said for other subjects, for a variety of reasons. For example, state schools have struggled to find enough - let alone really good - language and science teachers for years. That's a different filter. And compare the requirements for Chemistry to those of E&M: Maths at A grade for E&M; two A* in Maths and Science with Further Maths also desirable. There are a whole host of reasons why some subjects are less applied for but once at interview almost exactly the same level of competition is there in numerical terms.
I hadn't intended to run with this one, but other posters posted, so I replied.