I found it a big jump, I was top set GCSE and got an A* however I struggled a bit with Maths A level. What does help though is the modular system and the chance to resit, as maths is progressive in nature, by the time you are doing P3, you will find P1 stuff really easy as you are using the fundamentals so often, so you can resit and kill it. I did Maths and Further Maths so perhaps it was the pace of the course that I struggled with at first, rather than the subject. I ended up getting As in both though so it is possible to find something a struggle but still do well.