"Have DC's friends who have very wisely chosen more humanities based or less sciency subjects
Crazy, unfair system!"
But that doesn't help them at all where courses require specific subjects.
For example, I just checked at the university where I studied and their current requirements as to subjects are very specific indeed:
"Astar Astar A to include Astar A star in Mathematics and Further Mathematics"
Although, to be fair, for those not taking further maths they specify:
"Astar Astar Astar to include Astar in Mathematics "
So that may be a case where it works to do some other humanities (Back in the day, I did maths, chemistry & history and they were happy with that)
My DD actually did a very similar course at a different university, this is what they say now:
"Grades: A* AA
A * in Mathematics required. Further Mathematics preferred. If you are studying both then the A can be in either subject. Other preferred subjects include Chemistry, Economics, Physics and Statistics."