Unofficial observation from the control tower:
I believe you are right in saying that you only need to have studied towards A levels or equivealent to be considered accademic enough. You probably do need to have some maths skills though and at least a C at GCSE.
ATC is not an accademic career, but you do need to pass aptitude tests to get in in the first place. Some of these require quite good arithmetic skills, if not mathematical skills. Some controllers do have university degrees (and more), but many have few qualifications and still make excellent ATC skills.
I would suggest that you apply in order to assess the likelyhood of your acceptance. You probably don't get greater odds of acceptance by becoming an ATC assistant, but it would give you an excellent backgroung when you go to the college and train for validation. I would highly recommend this route if it becommes available, although there are no guaruntees of progression to controlling.
Unfortunately you are unlikely to be able to take advantage of your West Drayton location though...