You need to ask yourself the following questions:
1. Do you know what A-level English Language is actually about?
I'm sorry if that sounds patronising but many people think that it's similar to GCSE English Language, whereas it's almost a completely different subject. See here:
http://www.thestudent...lish_Language_A_Level
2. Why do you want to study anything at all (whether it be English Language or something completely different)?
If the main attraction of taking the course was that you'd enjoy the interaction with other students, then doing a home study course would seem to be rather pointless. However if you're really interested in the subject itself then there could be some value in home study.
3. Why do you want an A-level qualification? (Do you actually need one?)
If it's to help you get onto a university course, or to improve your c.v., then it makes sense to embark on a course leading to that qualification. However if you want to study English to (say) improve your novel-writing skills, it would be far more sensible to look for an evening class offering 'Creative Writing' (or something similar), even though there's no exam at the end of it.
4. Do have the self-discipline to study at home?
I've got a library book here on my desk, which I should have returned by today. I got it to help me to improve my Microsoft Office skills but I've kept putting off reading it. Perhaps you're like me?
Only you can decide whether home study is really for you, or not. I'd find the syllabus far too 'dry' for my liking and I doubt that I'd enjoy the course (or have the funds to pay for it!). But you might be different to me.
Chris