Hi Jo,
Do a search on this forum - you'll find a lot of previous very good advice on the NATS interviews.
My advice -
- Arrange a pre-intervierw visit to a unit and make the most of it, ask lots of questions and take what you learn to the interview.
- Know your aircraft types - it will convey your general interest in aviation.
- Be decisive - You'll be given "air traffic" problem senarios - They're no looking for a text book answer (that's why you have to go to ATC school

) - but come up with a common sense answer and don't change your mind just becasue the interviewer wants you to!
- Have an idea what else is going on in NATS and the industry.
Good luck, and don't be put off by what you might read on this forum - it's a cracking job!
PA