best distance learning web site for a levels? Watch
Khan Academy is good for maths and sciences, but is not geared up specifically for A Levels - still useful though, if you know what topic you are looking for.
I used NEC - national extension college for Biology A level last year.
Found it excellent. You are assigned a tutor that you can contact any time, submit assignments to and get feedback from. They also helped me with my coursework.
They have centers around the UK where you can sit your exams, so if you live close by to one it works very well, otherwise you have to arrange to sit exams at a local school.
NEC do help with exams but found their fees quite steep & locations very sparse. Was able to source a cheaper exam centre locally, just called the exam board & they sent me a list of centres in my area.