Math and Further Math => Math (As long as you you are good and interested enough to consider studying Math, Physics, Engineering, than this shouldn't be a problem for you. Otherwise you will learn the FM stuff in one or two weeks at University.)
Some internationals will also (have to) do 5 or even more A Levels, because 3.5 aren't allways accepted in foreign countries. (And they have to fight with the language in addition.)
Just try it and be aware that A Levels are not the most difficult exams you will take in your "academic career", but rather the opposite.
On the other side: Don't be to stubborn to realise if you aren't able to cope and ruin (you probabaly won't , but it can happen to everybody) your application.
Good luck!