How do sponsorships work? - they don't exist
Do you need a degree? - no, and I don't know of 1 airline that requires a degree (a degree is a waste of money IMO)
Is it cheeper in America? - yes
What else do you need other than a CPL? Do I need an IR? - PPL, CPL, ME, IR, MCC
Where's the best place to go? - only you can make that choice through research
Which A levels should I take? - sciences and math
Who should I contact? - flight schools for a look around, try to get work experience or voluntary work at a flying club
The big question to ask yourself: do you want to fly a jet from the moment you finish training until you retire (probably age 70 when you get to it)? It would get pretty boring. Too many people are obsessed with jets that they miss out on some great fun in other flying jobs.
You can either get an airline to sponsor
Only if your Dad happens to be the chairman of said airline.