BAC TSR.2
Capable of STOL, Mach 2 and also carrying a nuclear payload, this aircraft featured the best of British Aerospace engineering and technologies. Using the Olympus engines which powered the Vulcan Bomber before it, and Concorde after it, the TSR.2 is probably one of the best, most practical aircraft around.
Unfortunately, the programme was cancelled before leaving the prototype/experiemental phase. Good video on the aircraft here:
https://www.youtube.com/watch?v=PhXcd-881xA 