Yes, you can do a 1 year BTEC course.
I think you will achieve a subsidiary diploma at the end of it. But, seeing that you're already doing 3 A-Levels, it might be extra hassle for you to do a BTEC as well, because it's 100% coursework with various deadlines to meet.
Are you fully determined to do this BTEC?
Would you be able to handle it amongst 3 A-Levels?
Do you have time to do this BTEC?
Your other subjects need more attention, since A-Levels is not easy to manage and you need to get decent grades for university.
It's up to you. But, if you want to do s BTEC because it will help you towards your future career, then go for it.
However, if you're just doing it for UCAS points then I suggest that you focus solely on your 3 A-Levels and forget BTEC.
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