Well I can tell you as a recent graduate that universities are basically no different to secondary schools when it comes to their rigidity - in fact they're worse. You can do your A Levels at the age of 12, through your school, if you're enterprising enough. By contrast, I've not seen someone do a university degree in less than two years (and this was because they had graduated elsewhere); and by seen, I don't just mean firsthand.
Institutional education was a bad thing for me too: it rewards the hard-working. What's wrong with that? Well often it's not about intellect/creativity but rather your ability to sit in a room and memorise facts. Not just facts, but ridiculously useless facts. One of my exam questions was something like, "what is the sequence of enzyme bla bla" (I forget its name). I mean who the hell cares? Why would I need to recall that? You can watch Michio Kaku on YouTube echo my very sentiment - he did it for BigThink, or something.
I was in the same position as you, in a way, but I think I got lucky. I chose genetics and I ended up loving it (alongside evolutionary biology and psychology) and ended up with a PhD in a few months. Of course, maybe you won't be so lucky.
I really think that if you're unsure, mathematics is the best choice - and not just pure. Make sure it's applied, because then you can transition to a chemistry, physics or even biology masters (not to mention econ etc). Taking into account my PhD searches in the past year, mathematics was by far the biggest non-biology degree that was able to qualify for a position.
Tuition fees were 3.5k for me. I think they're 9k now, so I can imagine how worried you are about the debt. As I understand, don't you get higher grants now? They increased the cost to deal with the fact that they could charge middle-upper class kids the full amount without it affecting them too adversely. So perhaps your overall amount of debt won't be too different to mine (Taking into account living costs). I think mine are around 15k, but that's desperately easy to pay off assuming you do a decent degree and do decently well.
You can get student funding for OU degrees and plenty of people use them to go onto Masters/PhD stuff later. As for industry, again, I don't really know. My OU degree is something like 4,600 spread over 3 years because I am not English. I think for English people it is more like 15,000.