Hi! I'm also gonna be coming to Manchester this year for the mPharm course. As the previous poster said, I do think that chemistry would be the more important subject since that's the one they require in the entry requirements whereas biology can be replaced by maths. I also remember watching one of Phedra Dee's (a student studying pharmacy, though at kcl instead of manchester) videos where she said that pharmacy was really chemistry focused to the point where she could have conversations with chem majors and she also mentioned some of the topics that are major points of focus in pharmacy (of course take this with a grain of salt since she studies at a different uni but I'm sure there'll be some overlapping topics) so you could try watching that video.