"Our standard entry requirements are:
A-levels: A*AA in three A-levels (excluding Critical Thinking and General Studies) taken in one academic year. Candidates are required to achieve at least grade A in
both Chemistry
and at least one of Biology, Physics or Mathematics."
- Taken from Oxford. You DON'T
need three science/maths A levels - but you'll find some universities prefer it. I'd also advise if you're only going to take two science/maths, to let your option be Biology (chemistry is a must) because some medical schools require both Chem and Bio:
E.g. Imperial
"Our minumum entry standard for 2019 entry is
AAA overall, to include:
Law has no specific requirements, though sometimes an essay subject is reccomended.
Chem,Bio, Maths and English lit would work superbly - or even just Chem, Bio and English lit would be fine; you don't need four subjects necessarily.
A very few unis strongly encourage three maths/science subjects...
(Cambridge) "Please note that in the past three admissions rounds, 98 per cent of applicants for Medicine (A100) offered three or more science/mathematics A Levels and, of these, 31 per cent were successful in obtaining a place. Of the 2 per cent of applicants who offered only two science/mathematics A Levels, 8% were successful in gaining a place."
...but most unis don't require it.