So there are no prep classes or anything like that in the UK. Everyone sits the same set of exams (modulo being Scottish or English/Welsh/NI, which have different types of qualification) and those results dictate whether you can go to University or not. I suppose you could study more if you wanted?
Rich parents can of course help their kids be better in school, but there is no efficient exam prepping.
The last two years of school are generally a prep course for the German SAT equivalent (and grades in those two years account for around two thirds of the final score).
In which case schools located in areas with a higher cost of living are effectively receiving less because any teacher working their, while on an absolute scale making the same, is making less on the more realistic scale that adjusts for cost of living.