Combination to be a Computer ScientistWatch
It really depends on what you are going into, you'll almost definitely need physics and maths for engineering, or maths and computer science for a more cyber orientated degree, but taking physics maths and computer science gives you a broad set of career paths and can basically get you anywhere in the industry. If you are really good at maths and want an edge, further maths is also a good option. Hope this helps
A Levels are primarily your stepping stone to get you into university, onto an apprenticeship, etc. So look at the university courses you want to attend, see what their entry requirements are and go from there. Some universities have no specific subject requirements, although A Level Maths is a very common requirement for CompSci degrees. Of course, the tech industry isn't just about Computer Science.
Further Maths makes u better application but its not a prerequisite whereas a-level maths is usually a prerequisite at most places.
And then a science.
So maths, a science and a third subject will be completely fine.