The problem with making valid ATCOs redundant is that you also have to stop all training as these trainees will replace the now redundant ATCOs. And that is illegal I believe. So valid ATCOs are generally safe. Even units which are probably overbearing due to the fall off of traffic cannot loose ATCOs as if there is an increase you cannot bring any trainees in for 3 years I think. However this may be complete rubbish so I await someone who knows a lot more to post so that I can be educated as well.