What license do RAF Pilots need to fly a Fighter Jet. ?

In the military you don't really worry about licenses. Some military pilots do get civilan tickets just so they have them when they later get out of the service. However, in the military (my experience is with the US) you get checked out in the aircraft (sometimes called a "Form 5" in the US). There is usually a progression so if you are checked out in a tactical jet you started out in a training aircraft. However, its not necessary to join the military with anything other than a 4 year degree and good scores.