If I can offer a few words of advice - I am not a pilot but know quite a few and have also been through the recruitment process (coming 22nd in a process where 21 were offered a place on a training scheme!)
I was very impressed reading your post. It seems you have a level of maturity of someone quite a few years older; you seem to know exactly what you want to achieve and give the impression of not being phased by the hard work needed to get there. The grades you are outlining should be enough to meet the academic requirements needed to get on a course.
Just a thought, but you might wish to consider a business-related A Level (such as Business Studies) as airlines, particularly BA are looking for pilots to take an interest in the business itself as well as the physical flying of the plane, and see how their actions outside of the flying can fit into that. If you were to use airlines as case studies in your coursework and brought that up at interview that would surely impress.
Secondly, I am sure you will, but get a thorough understanding of the technical aspects of flying, such as how a jet engine works and why, for example, it is more efficient at altitude. This is what tripped me up at interview.
Thirdly get a good understanding of how airlines' SOPs work as there will be questions along the lines of "What would you do if....." in the interview. Interviewers are not necessarily testing you on the intricacies of the SOPs but looking to see if you can make calm, rational decisions in the face of unusual situations. Understanding the SOPs will help you to understand the mindset.
Finally show that you are passionate about flying by getting some flying lessons under your belt. If you can show in the interview that you have, for example, worked weekends to earn money to pay for lessons, that will show a level of determination above and beyond some of the other candidates. Alternatively join the air cadets.
Above all else, echoing the advice of Wiggy, one of my mottos is "Always have a Plan C" and never ever give up on your dreams!
Good luck!