RimBim,
It all depends what threat you're training against. ASDOT has already suggested that the retained T1 Typhoons will be the "need peer" Gen4/4.5 threat emulators, but there are plenty of airforces flying older aircraft still, including several flying subsonic FGA aircraft which the Hunter can quite adequately replicate. As with all T&E/Red Air Opfor it's also dependant on the kit; we used to use the Cobham DA20s to replicate BVR red air when the F3s/Typhoons couldn't provide. With the right operator in a surrogate airframe with some clever emulation, an awful lot of good training can be achieved at relatively low cost.