Shipway,
I am no expert on this, but I believe that the questionnaires are in place in order to ascertain how you approach learning, problems, life etc. When I was going through the selection, it was the one thing that I wasn't worried about failing on. This wasn't because I knew I would pass, but, if I didn't it meant NATS thought I would have struggled as a controller and may have given up my career only to fail as one.
Try not to be to disheartened, as it is certainly not your intelligence that let you down on this occasion.
Regards,
RO13ERTS