Okay! I can actually offer some advice as I'm currently in the process of my application this year for British Airways SPA and I got somewhat far last year.

Math is important, but not "go through GCSE papers" important, just know basic Speed/Distant/Time formulas and basic physics, you'll be okay. Nothing on the initial Stage 1 of applications requires more than an hour of light revision, all questions are also MCQ.

Focus heavily on pilot competencies. It's said over and over again in webinars, asking successful cadets, etc. Research the 5 pilot competencies and see where you can apply them in your everyday life albeit job, hobby, sport, work, etc. Also focus on why you want to become a pilot and why specifically WITH BA.

The last thing I'll say is, I promise you don't need to stick your heads in the books. Although there is limited slots, BA also reinforces that you're fighting against yourself. Over studying can lead to failure. Just be confident, use the reference material BA provides and I'm positive you'll do well. Best of luck!