I haven't done any of the FEAST tests so can't comment on any possible mathematical comment in those, but the only time maths comes up in the NATS tests is the 'collision and concentration' task. The maths there is a distraction - if you can answer some of the questions thrown at you while completing the main test, good on you, but it's not absolutely necessary.
I have A-level Maths (and quite a bit beyond that) and didn't need any of it for the NATS tests (it also wouldn't have helped me in the slightest). The maths asked of you is something like:
3119472
9628 x 324 = A. 31984 B. 2708851 C. 3119472 D. 4563785
You have approximately 2 seconds to answer this(!). A tip I got from a current ATCO is if you're given a multiplication, just multiply the last digit of each number, as the answer must be the last digit of the sum (in this case, 8 x 4 = 32, so you're looking for answers ending in 2). Same tip goes for addition/subtractions.