If applying to study law at university, you will need to take three A levels (no more than three). Most universities do not stipulate any A level subjects for law applicants, but check the website of each university which you are interested in.
To be a competitive candidate, pick three rigorous academic subjects that you are likely to be good at. A language A level is always useful.
History is a very useful subject for those who wish to study law. It is notable, by the way, that amongst the approximately fifty percent of lawyers practising in the UK who do not have degrees in law, the most commonly held degree appears to be history.
SB (lawyer with a degree in history)