Just picking 1 I think could be tricky! I took Chemistry, Biology and Geography to A-level and Physics to AS-Level. I certainly enjoyed Chemistry the most but if I could choose again I would definitely have tried harder with Maths (maybe taking that instead of physics). So much of the work I do now needs me to decide whether my findings are reliable, and that requires a good knowledge of statistics.
I’d recommend maths (universal for almost all sciences), ICT or IT (you’ll likely end up using computers, and will probably need to program them), and one of the sciences you are interested in. If available – take philosophy as well, critical thinking plays a significant role in scientific endeavours.
In any case, check relevant university courses – they usually list what subjects they need before they can accept you.
answered on 26 Jan 2018:
Mathematics (and further maths) – these skills apply in so many areas of science but also in other areas of work as well. I think mathematical/statistical analysis is the ultimate transferable skill. It’s how to turn data into knowledge!
You really need more than one A-level to get on the track to a career in science, and this will depend on the specific area you want to work in. But whichever science you go into, you will always need maths – so make this top of your list!