Check out requirements for unis - I have seen some which say they are happy to accept the BTEC extended diploma, but some want additional A-levels, and some say they will only accept it if you haven't sat A-levels before.
You also need to ask the college about funding. I think you will have to pay as you have already done 2 years of level 3 study and gained 3 A-levels, but it's best to check with the college.