Baggage handler, Information Desk personal, check-in personal, there are many jobs within the airport facility that you ca work with. I don’t know about what educational background they require you to have in the UK, but I’m sure if you do some research, you’ll surely find something fun. If you are interested in Service-minded work, which basically is the biggest and main aspect of working with transportation and in this case, planes and in an airport/airspace, then there are endless choices and opportunities no matter where you are in the world and no matter your grades and all.
I’ll say, you’re 14, you are still very young, I’m turning 19 soon, I for a few months ago, I thought, hey, what’s the purpose of even studying is all good high level/class educational programs and studies are for those who do well in elementary and high school. My grades don’t match up to those at prestigious universities… I honestly cheated my way through 3 years of maths, thanks to my friend, we all basically cheated, but we all, me and my friends, now with our high school (Secondary School, Year 11 in the UK, equivalent) graduation coming up soon, we all know where to go; with some to university, others will take a break, and the rest might start working with something before find a new path in their life. That isn’t to say you should cheat on exams, but that as times goes on, and you find alternative ways to pass hardships, in the end, you’ll know what you want to do in the future.
So focus on school as much as possible, the extra bit of learning, better results on exams and understanding what the school is teaching you, will boost your knowledge, your educational background, yourself, and it may be the little push in the right direction for you to find the job you want to have in the future :)