Brilliance in Maths and Physics will certainly assist you to some extent in your application but it is far from what is required. A basic understanding of Maths & Physics (GCSE level) is all that is all you need.
To be successful the two most important factors are motivation and demonstrating that you are the kind of candidate that British Airways are looking for. Your motivation for the role will shape your whole performance throughout the process.
Having strong leadership qualities is just one of the skills required to be successful. You also need to be a strong team player, a good communicator, a good problem solver and have the ability to remain level headed and calm in pressured circumstances.
These are just SOME of the qualities required. There are others but these qualities carry a lot more weight in the process than simply being brilliant at maths and physics.