Phil and CJ. With respect, you both need to mug up on civil and military ATC. The guys working in RAF ATC Units are not simply ATCOs working for the RAF as civil and military ATC are similar but different ball games.
If you are interested primarily in a military career, with all it entails, then go for the RAF or the RN. If you are just interested in ATC and want a quieter lifestyle with much better conditions then go for NATS. Check on what RAF ATCOs earn and how much time off they get...... where they're likely to be posted, etc.
Good luck to you both.