If your college offers law A level or even law BTEC, I would say Law, Economics, And Maths is the best combination for both degrees if you haven't made up your mind yet.
for Law: Law, Philosophy, and Maths is a hood combination as admission tutors love applicants with maths as they believe mathematicians have really good analytical skills.
for Economics: definitely Economics and maths. Your thirdwouldn't really matter however any thing related to economics will be a bonus. A language would come in handy so maybe Spanish.