Further maths. My physics A-level had a practical exam, which was harder than the written paper for me. But further maths required more work... especially FP2, which when I did it was hyperbolic functions and advanced integration. I had to work through every single exercise in the textbook to feel confident enough for the exam.
They've since re-jigged the syllabus so it's no longer all together I gather. At the time it just seemed all the hardest stuff was in one module.