If you have access to the Open University then your options are unlimited. I completed an LLb (hons) with them whilst flying. Mainly for the reasons you specified and I have always had an interest in Law and it has given me a very good overall knowledge in lots of different areas.
Another person I fly with has just completed his Psychology degree. Mine took me 6 years of nice 'relaxed' study, he has done his in 4 years with a bit more effort.
Just go for it, with the OU you will find there are some subjects like humanities and sociology which are nice ways to introduce distance learning and count towards most degree courses, why not just give one a go and decide which way you want to go once you have a 'taste' of what is required.