Definitely do maths! I started out doing maths, biology, chemistry and psychology but later dropped psychology (before the AS Exam) as I didn't like it much. I hadn't done it at GCSE either but I thought there would be more science content in it. A lot of it wouldn't help with a medical application. Obviously this may be slightly different depending on the exam board.
However, a lot of the time universities will ask for "Chemistry and two other science based subjects". These are always biology/human biology, physics or maths. Subjects like further maths, sports science and psychology are often not accepted as a science based subject. This means not doing maths would cut off a lot of options for you.