Ronnie
Despite ORAC's last post I believe nationality requirements have now changed. You now have to be a British Passport holder/citizen to join the armed forces in some (if not all roles). If NI then OK, but if you are "Eirish" you may need to apply for dual nationality. I believe it has more to do with coalition operations than UK requirements. Many of our ops are now joint so you have to be able to meet the UK/US Eyes Only requirement, the US get very twitchy about RAF/RN/Army personnel who are not UK nationals. I suggest a phone call to OASC at RAF Cranwell, or any careers information office would be your best course of action.