I am going to give an answer you won't like but I'll be honest. From what I read I am not sure if you understand what the FPP is exactly. I'll cover that in brief at the end.

Do not give up education for a chance on the FPP. Go to university first and apply for the programme after. If you feel any less about flying after graduating, do not apply for the programme. Firstly, suddenly feeling a bit detached from flying is a sign dedicating years of your life to flying is not a good choice for you. Secondly, think of flying as a lifestyle and not a career. You won't have regular periods of time at home, you won't be able to have your wife's or children's birthday off work (you probably won't even see them on their birthdays), you won't have every Christmas or New Year off etc... For some people this is fine but for others it's a hard push. Ask yourself, is that what you want? It's easy to fall in love with flying. I had a taster lesson on my 17th birthday. After that I decided being a pilot was for me so set about my PPL. I then stumbled upon Pprune which forced me to realise I had fallen in love with the idea of glamour and flying, and not the career. There's a big difference. I chose a different career option instead. But I am considering a switch. I do not enjoy what I do.

Also consider how you pay for it. The FPP does not provide free training for you. BA will offer you a provisional job contract provided you complete training. The school BA sends you to for training will require a bond of £84,000. The bond will be taken out against you; not BA (BA provides a loan if you like). If you leave training or decide not to be an airline pilot, you will have a big bill at your feet. BA will only repay the bond in monthly installments over the first 7 years as an airline pilot for them. If you do not like the job, 7 years is a long time to stick it out to repay the money.

If you have read this and are still enthusiastic about flying, go for it, but after university. You need a fall back option just in case you dislike the career.