If you go to Uni first which is what I did, I wouldnt worry about the debt side of things to much. I was over £13k in debt when i left 6 years ago this summer and as of next month will have paid it all off.... and life has hardly been a struggle doing that.
I applied and got in at 17 and turned it down. Spent a year out travelling a little, followed by 3 years at uni for the sole purpose of drinking, having no responsibilities, playing Nintendo and enjoying a second home under a table in the student union.... which is something that I wouldnt change for earning a few grand extra a year. I reapplied and went through it all in my 2nd year at uni and got in again with a start date 4 months after i finished uni.
Training for ATC is bloody hard, so if you want a few years to basically dick about go to uni..... dont jut think of the money. If you get into NATS and validate you will have enough of that, its about the experiences and if thats what you want then go for it.
If you are an ATCO for 30 years.... no harm in waiting 3 to have a little fun while you have no job to loose if you turn up wasted, something that seemed tolerated at uni but not at CATC
Whatever you choose, choose it for yourself, not what any of us on here say..... just dont have any regrets and you know you made the right decision.