A couple of things to consider:
The course is not easy and validation is by no means certain (far from it)
if you get through the selection process and join the college. Being keen and putting in lots of work will not help if you just don't have the aptitude.
If you join NATS and find that you fail to validate 3 or 4 years down the line what will you do? Will you really feel like going back to uni after 3 or 4 years of intensive learning... especially as you will have been on a wage with NATS and you will have to revert to being an impoverished student again (or should I say,
more impoverished).
If you go to uni first, you will find that (in most cases) you will emerge a slightly more mature and rounder person - this will hold you in good stead for any ATC course. Waiting those extra 3 years will not make you lose any aptitude with regards to the selection tests. Of course, being more mature will not guarantee sucess, but it will help when times are tough.
Finally, forget ATC for a moment... just what do you envisage doing with a BA in Geography? Is it a degree you have chosen with a specific aim in mind?
If yes, I would be inclined to got to uni first, get your degree, then try ATC. At least then you will have a fallback plan.
If not, I would consider all the advice on this thread. You do not need a degree to suceed in ATC - NATS alone is littered with examples of this fact.
Good Luck
