As I am currently nearing towards the end of my GCSE journey, I have started to contemplate my future plans including things as close as the summer holidays as well as even as far ahead as university. One of the main things I have decided I would like to achieve in the near future is success in the British Mathematical Olympiad, therefore I am hoping to spend the upcoming summer holidays practicing for this prestigious mathematical competition, by working through the past papers as well as some olympiad-math based books.
I was wondering what books, except the obvious ones like 'A mathematical olympiad primer', would help me in building up my mathematical competence in both providing me with the theory required for such difficult competitions as well as a wide range of problems which would help me to build up my skill in finding solutions to the problems.
n.b. I have experience in the intermediate Olympiads (I am aware it's a big step up) and have a steady knowledge of topics covered like combinatorics, number theory, geometry and algebra.