2 questions, so two answers...
1. As long as you have a good answer at interview as to what you've been doing during a gap in your CV, it's unlikely to affect your assessment. I had been unemployed for 6 months when I applied to NATS, but I got myself into a postgrad course just before submitting the application and it worked for me.
2. Where you live now has no bearing on where NATS will post you. ATCOs are in a mobile grade, and the stories of people asking for "anywhere but Aberdeen" and being posted there are legion. In reality, you have probably a 70-80% chance (if successful) of being posted to Swanwick.