I am currently about to begin self studying for UK maths a-levels, however I am also wanting to gain a solid understanding of calculus. I know that calculus is covered in a-levels, but, the books for a-levels seem to be not as dense or as good as the US books I believe. 

My question is this. Would a calculus book better explain calculus than general maths a-level books? And would it be a wise decision to study primarily off a calculus book and fill in all extra gaps required for a-leave in the a-level books?

Any advice would be very helpful. Thanks.