Do not try to specialize so much, if you find yourself disliking it (what you enjoy as a hobby, you may not enjoy as a career), then you're pretty boned.
As for college, don't waste your time on that BTEC. The best plan when you go to college is to get a wide variety of a-levels, and then go down the path you enjoy most at Uni.
At my college, I could take 4 A-Levels (+ general studies 1/2). After the first year, most people dropped one (and just kept the AS grade), but if you didn't want to, you didn't have to. Going by this, and knowing you want to spend time in the game industry:
1 - Math
2 - Computing (forget IT, pointless).
3 - Humanities/Language Course
4 - Art/Design Course
If you're good at a foreign language, take that up as an A-Level, if not, stick to a humanity. As for which humanity, up to you. I find both History and Politics fascinating, but require good writing skills. Economics is probably the most important humanity out there (in my opinion), and most courses don't require amazing writing skills - if you flunk out on maths, some lesser unis will accept economics as a proof of numeracy. If you're really interested into getting into gaming, you might want to consider looking at AI programming, in which case, philosophy will do you really well, going into uni.
If you find pure maths boring, it would be acceptable to switch it into physics, most unis accept that (physics is NOT an easy course, though, don't be under that impression).
Anyway, these are my recommendations as they give you the skills you need to go to uni and study many courses relating to game development. At the same time, it also gives you a couple of fall back courses in case you find that you don't really want to do it full-time, after all.
As long as you have a good A-Level in maths (or related), you will be able to take 60% of uni courses out there (providing you don't flunk other modules), an A-Level that proves your ability to write will probably open up the remaining 40%.