You are still young dude! Best thing you can do right now is to finish your A levels in maths and physics (preferably) and then do a degree for 3 years (Bcom or engineering degree, or whatever suits you). Then work for some time and understand how hard it is to earn a living in this world and then you'll be in a position to make an educated choice as to what route is best for you. It's much better to keep the flying part for the end. Oxford will always be there and if not there will be others to replace them...
You have plenty of time to achieve your dream. Do some research about schools and take a few flying lesson if you can. How you feel about flying is the same for all of us but you have to be patient and not burn any steps on the way.
Keep an open mind and look at other career path that might suit you in the event you can't fly no more. As you are aware you have to do a class 1 medical every year and too many people seem to forget that if they loose this that's it... end of career for most pilots especially if you are still young with low hours, thus the importance to have a back up degree. Future employers would also prefer to see that they are employing someone that is educated and not just with an ATPL. Airline operations nowadays are more complex and pilots have to play an essential role in the financial savings that they make at the end of the year...
Much better to do the degree before the flying than the other way round or when you are facing the medical problem and have a family to support. Life is full of surprises and don't be stubborn into the idea or dream to be an airline pilot...It's stupid!! The way you see things at your age is a lot more pleasant than it really is once you have to work and support yourself, let alone a family.
And please, above all don't put your mum into this equation it wouldn't be fair on her to have you decide on her future...
