Chemistry isn't really relevant for biological anthropology - it's not biomedical sciences; outside of some basic elements of material composition and isotope dating there isn't anything relevant for the vast majority of biological anthropologists (or archaeologists, for that matter) who don't normally do especially detailed physiology work. Any option is really fine though, just pick whatever you're strongest in - if this is chemistry that's fine, if not then don't take it (particularly as A-level Chemistry is not an easy option by any means). That said, Dundee's course is in forensic anthropology, and might entail more chemical elements than a typical biological anthropology/human sciences/archaeology course as such (but I still doubt it, looking at the course structure).
Outside of that particular course, since biological anthropology is ostensibly a social science, or at least closely related to social sciences, taking a social science option might be sensible (although having essay writing background from English lit will be sufficient, you might develop the kinds of thinking used in social analysis more with a social science option). Something like sociology or psychology might be relevant and of interest, for example. Alternately, languages are always useful, particularly if you wanted to continue in academia in anthropology generally.