A strong Mathematics and Philosophy personal statement should not read like two separate mini-statements. Use one or two connecting ideas: proof, infinity, logic, probability, explanation, paradox, or the nature of mathematical objects.
For this course, proof-writing and philosophy-of-mathematics reading can work together: a paragraph about a corrected proof, a definition, or a foundations question can show the same habits that TMUA and interview problems test, precise reasoning, explanation and willingness to revise an approach.
Avoid listing books without showing what changed in your thinking. A sentence explaining why you rejected a first interpretation of an argument is usually stronger than another title.
Use mathematics to show method, not just achievement. A short discussion of how you approached a hard proof, corrected a false start, or made an argument clearer is directly relevant to the interview style.
The UCAS personal statement and academic reference are part of the evidence considered in the application.