Have you had a look at
http://www.open.ac.uk/
They do all sorts of subjects and mix and match which leads onto a general degree.
I have always had an interest in geology and fossils and the like and have just signed up for the "starter" course in fossils. Which in reflection and reading the book with my spelling ability is going to to be fun (everything is called something with about 9 letters).
Myself I don't know if I will complete until graduation. But the courses are extremely well written and easy to use.
MJ