JonathanB good choice, im sure you have made a the right one.
Those of you who have your stage 3 and you want to prepare some answers etc... NATS new careers site has a pdf of info on all stages. In stage 3 the sections listed are the sections they will ask various additional questions to, They want a situation for each one and will ask further in depth questions to clarify your scenario. The link is here
http://atcocareers.co.uk/pdf/Hints-a...Three-Days.pdf
Good luck to all