All the Sciences and Maths (Further Maths) are just a bit too tedious and do not reflect the candidate?s knowledge and understanding of the wider world, IME.
Another essay based subject he may consider is Divinity/RE. Personally, I think this is much more relevant than History, Geography, Language, etc. in a field like Medicine. Don?t be mistaken, Divinity isn?t all about God and the great Divine in modern day exams. It has plenty of (medical) ethics questions, for example:
Q: Has a 70-year-old woman the basic human right to bear a child of her own? [Through IVF, of course!] 
Q: Who in your opinion, has a better legitimate claim to a NHS liver transplant between a confirmed alcoholic (family man with 3 young kids) and a young bachelor?
Take a look also at OCR?s Religious Studies A-Level paper from January 2011:
-
Critically assess the claim that conscience is the voice of reason.
-
?The environment suffers because business has no ethics.? Discuss.
-
?Our ethical decisions are merely the result of social conditioning.? Discuss.
-
?Natural Law is the most reliable approach when making decisions about premarital sex.? Discuss.
Preparation for RE A-Level bodes well in Medicine interviews. DS has a particular knack for this subject which he took to A-Level (A*) together with the Sciences and Maths.