I agree with High Wing Drifter. You're young, so you've got plenty of time. Go get a degree in something employable (if nothing else it will help you pay for the training). It doesn't need to be aviation-related (as HWD says the ATPL writtens aren't rocket science) but it should be something you are interested in. It's very hard to do well in a degree subject that doesn't inspire you.
It's worth trying to save up a bit of money for a few hours before committing yourself to that fATPL, strange as it seems some people get started flying and then discover it isn't for them - might be worth posting on Private Flying to see if anyone will take you flying too. Plenty of PPRuNers around London and people are usually happy to take a passenger. Good luck!
