How to apply for access courses at university or college?

For a long time now I've really wanted to attend Uni and it's always been a dream of mine to study at UCL, however due mostly to extremely frequent relocation I missed an awful lot of school, ended up coming out of school with only five GCSEs I think (Math (C) and English (DD) and science (CC) and screwed my first few years of College up doing btec course. i have now a huge interest in science and that part of my life.