add maths igcse & a level maths

my school only offers a limited range of subjects and add maths was not one of them. im taking my exams this oct/nov and I'd like to have one more igcse subject on my record, and I've already decided to a/l maths.

I want to know if taking add maths while doing my a levels at the same time is possible. if so, will studying it be easier, as i will be taking a/l maths anyway?