Thanks for the replies.
My thinking was actually that a very light jet could be useful for basic flight training - before the Tucano. To be honest I didn't think there was much of a market for such an aircraft in the Military anyway but thought it might be worth asking.
I am designing a light 1 or 2-seat jet for personal use. It's based around a glider fuselage (with appropriate modifications of course) so is a very cheap alternative to the typical jet-powered aircraft that consume lots of fuel.