To add to the advice already given:
A lot of courses (such as GCSEs) are part time / evening to enable people to work full time.
You need to really look into what financial support is out there. I'm not clued up on funding for Welsh students at college. However, the college you intend on studying at, will do.
If you do an Access course for example, these are aimed at people who work. They're (mine was, anyway - it's probably changed since then) usually 3 days a week, which allows you to work part time as well.