Hi
Not sure if NATS are recruiting at the mo but can't hurt to have a look at their web site for more details.
Aviation experience is helpful, you'll have a better understanding than I did when I started!
As for training. I was training for 18 months at the college, I'm not sure if they've revised that or not but it takes time. Felt like a lifetime!
I wish you all the best with it. Go visit a few towers or come and see us at TC.
Good luck.