Think of the Royal Navy and the Army as well. Army will only be rotary, but fantastic aircraft (Lynx is superb I understand, though I have never flown it) and I personally loved helicopters.
If you definitely want to be a pilot (get at least one lesson before deciding - believe it or not people start courses then find they hate it) then go for sponsorship as soon as you have A levels. Then you get all the chances you can. If you don't want to do a degree then think about other airline jobs while your waiting to fly - you make contacts, and can be elligible for internal sponsorships, while earning money and possibly travelling too. If you don't get sponsorship consider a degree, do something for a "second choice" career. As a pilot the subject is unimportant, though a scientific/technical degree will help keep you numerate for the ATPL exams.
Any more specific questions feel free to email me - I am ex-military and now work for a commercial flying training school. Best of luck!