I did (the old style) AS-levels (which I got totally crap marks in), and then an Access course a few years later. I got offers from some good universities on the basis of my Access course (Durham, Newcastle, Sheffield, etc), having achieved Distinction in every module. I didn't find the Access course very difficult, but then I also didn't find university very difficult.
I now work at the University of Cambridge, and we definitely accept Access to HE as an entry route for mature students. A-levels aren't even available to mature students in many parts of the country, and tend to be prohibitively expensive compared to Access, when they are.
There are some subjects which require A-level Maths. In this case, you could take an Access course and just the one A-level, which would probably be cheaper than taking 3 A-levels (eg if you did maths via distance learning).
On the other hand, some Access courses are suitable preparation to study Medicine at Cambridge, without any A-levels needed.
Anyone making the choice between Access and A levels should contact the university(/ies) they are interested in beforehand.