Jay,
Hi, I am joining Bournemouth in September, and am changing careers to do it.
I went through University, and have a degree. You will not have to pay back your loan while at college, because the basic is below the payback point. You will once you go out to a unit the salary is above it. But do not worry about the student loan - it's like a tax, you only pay when you earn. (I wonder if HR could pay us in expenses - they're exempt!)
From what I know now, having been through the application process, I would say go to University first. I know how you are feeling because I felt the same way... I was fed up of study and wanted to get out and earn money.
The reason I say go to university, is I am now well aware that you have medicals and scrutiny of your decisions to deal with. Both of which could end your ATC career at a moments notice. If that happens you will at least have a degree to fall back on. Also univeristy is a great experience and will teach you many life skills that you may not get going out to work straight away... like how to live with no money, a packet of corn flakes and a bottle of tomato ketchup... (At uni you will end up in that situation!)... BUT pick a useful degree - i.e. one you can use out of the box so to speak. There are many out there you require almost another degree in study before you can use it... Film and TV for example.
Hope that helps. Remember though it's your decision.
Laters
Jon