Looking at a table like this, though (from 2018-19), it didn't seem like most of the thinning out process at Durham - between offers and admissions - happened through students not achieving the high A level grades required, but through students not accepting the offers in the first place. So I'm quite confused.
The table is from Durham's website, under admissions statistics and under the heading Office for Student Transparency. It shows between two thirds and three quarters of applications receiving offers in the 2018-19 cycle, with only 17-18% of those who applied accepting the offers.
So if that's where most of the 'wastage' occurs, as with most non-Oxbridge universities I guess, why would they need to cut back offers as drastically as it appears they might be this year?