As above, for the purposes of admission, facilitating subjects are now irrelevant. Subjects will be clearly listed as either ‘essential’ or ‘recommended’.
That said, related subjects can be useful for understanding whether you would actually like to take a subject in HE and also give you a base level understanding to build on. It’ll also likely be easier to write a half decent personal statement about a subject that you have some familiarity with.
Unless Maths is essential, (and it can be for many degrees), there’s not much point in taking it if it’s going to be a weaker subject. Better to get a decent grade in something you enjoy.