By the way if you are basing your career choice solely on watching CSI then I can warn you- its nothing like that in real life. Ive done work experience with the SOCOS at my local police force and it was totally different, and nowhere near as glamorous or exciting as it seems on TV.
If its a SOCO you want to work as then you're better off doing your A Levels and then looking for vacancies, as they will provide on the job training.
I am finising my Forensic Science degree this year (accredited by both the RSC and FSS by the way) and then going to do my MSc this Sep. Its in no way as easy at it looks, with loads of chem and biol involved, so you need a strong science background if you are thinking of doing this degree.