How many ucas points do you have at the moment?
You could do the BTEC 90 Credit Diploma that's 1 year, check how many ucas points the grades are worth. When you add it all up with your A levels if it's enough. You will get two grades, for 2 years it's 3.
If it's not enough, then unfortunately you will have to do 2 years.
Edit: just noted you've not done two years of A levels, just AS. I'm not sure AS has any ucas points.