Regardless of whether Psychology is acceptable as a science subject or not, most bioscience courses require Chemistry, and if they do not you will cover a signifcant amount of A-level Chemistry in the first year. If you are contemplating changing a subject, that would be the best option to change to, strictly speaking. Mathematics would be acceptable for some bioscience courses, and is useful for Psychology and less molecular/cell biology focused Neuroscience courses. It is also considered "useful preparation" for Human Sciences at e.g. Oxford, UCL etc.