A-Levels and BTEC

So, I was an international student in school, and I came to the UK last summer (2014). I immediately started college, and my interest in IT got me in BTEC L3 Extended Diploma for IT Users (it was suggested to my by the staff of the college). Not knowing what exactly BTECs and A-Levels are, I started lessons on September. I also got enrolled in AS Maths in the same year, since I was told it is going to be helpful for Computer Science, which I want to study.
Now I know how the qualifications work, and I think I shouldn't go for BTEC, since I want to get to a top university (e.g. Oxford or UCL). Obviously, they show preference for A-Levels.

Should I drop out my BTEC this year (first year) and choose more A-Levels to study from next year, so that I can have more chances in these unis?

Oxford: Computer Science: BTEC IT DDD +A* A level Maths

UCL don't for CS (although I'm sure they would with A level Maths) but they accept DDD in IT for their Information Management course (No A level required)

Also other top unis for CS accept the BTEC like: Southampton, Bath, Birmingham, Durham, Bristol, Manchester and KCL to name a few

Personally if I were you I wouldn't waste the extra year or two, also with the BTEC you get a lot of practical experience which is favoured in industry and It depends on what units you're taking but if you take all the programming ones youll end up with more programming experience than someone with Computing A level