How much do my IGCSEs matter?

My IGCSE's aren't necessarily bad but they're not good either (definitely not Oxford standard). A lot of my grades were lower than expected (specifically international maths, both English courses and French).
Even if I were to do much better on my IB Diploma, would it still be a deal breaker? Would I be severely disadvantaged, even if my IB results might look okay on their own?
(I'm applying for mathematics. Also, I'm not a native French speaker and I'm not in a French speaking school, but I don't know if that makes the C look any better.)
My grades were:
International mathematics: A
Additional mathematics: B
Coordinated Science (Double award): AA
Music: A*
First language English: B
English Literature: A
First language French: C (what even happened here?)
Foreign Language German: A*
Is it possible to not submit my IGCSE results so that the examiners won't see them, or is it required? Do the examiners automatically have access?