Chances are whatever you start out as won't be what you'll be doing twenty years or so down the line.
If you're really not sure yet what you want to do (and at 14 I wouldn't expect you to be), then for now just do courses in subjects that interest you, or that you enjoy. If you have to take a course you don't like because that's what you need for a particular job, chances are you won't like the job either.
Also, don't give up your outside interests for GCSE study, as so many people seem to do. You need the distraction, plus those outside interests may be the catalyst into the ideal job for you. Top exam grades aren't the key to getting a good job, despite what you may be told. Believe me, no-one wants to employ an exam bore. Your attitude and personality are far more important and if you don't get into university, then maybe it's not for you after all.
For now, just enjoy what life has to offer you. Do your best in whatever you do, and if you can get out of something you don't like, then do so. Those who matter, won't mind, and those who mind, don't matter.