(Original post by Hippodamos)
I would definitely recommend OU study if your study skills are good and you are an independent learner. If you can motivate yourself and put in the time, then the chances are you will do well in assignments and exams.
If you are serious about applying to Cambridge/Oxford, the OU is a good route - I have an offer based on my OU study. I did 90 credits at Level 1 and 60 at Level 2, over two years, but you probably wouldn't need that many. They want distinctions (>85%) though, which is hard work considering exams are involved.
But I think that is one of the strengths of the OU in terms of applying to other universities afterwards - you have real exam experience and have been developing the skills necessary. My understanding of many Access Courses is that they are mostly continuous assessment, which is nice if you want a string of starred Distinctions but a bit shortsighted if you manage to talk your way into Cambridge and then realise you've not taken an exam since you were 18 and you have to try and figure it out at the same time as, you know, doing the degree.
I wouldn't recommend jumping straight to a Level 2 course. Go with a Level 1 course, perhaps something you are already familiar with. This gives you the chance to get used to the OU system and working on your own.
One problem with figuring out that you want to make changes in your life is that, at the beginning, you're full of ideas and plans but not yet actually doing anything. So in your mind you think "Oh I will just do a few Level 3 OU courses, work full time, do some volunteer work, run a marathon and apply to Cambridge by October." when really you might benefit from slowing down and being a bit more realistic with the expectations you place on yourself.
In summary :
If you are capable of independent study, managing your time and generally being responsible for your own education : go with the OU.
If you need more face to face support, to brush up on your general study skills, to be told what to do : go with A levels/Access.