In use by AGS (that's Army Group South) (I think it was them...) at the Queensland Living History Federation's History Alive event a couple of years ago. I don't know much about it except it was cool and was actually working!
Development of the Churchill, the idea leading to the much more succesful (albiet similar looking) Centurion later in the war. The Black Prince was a prototype only.
TOG2 - The Old Gang tank
British prototype built for WW2 in expectation of trench fighting. Never happened, so neither did the tank. Originally designed to have sponsons to either side and drive slowly (but ever onwards) nigh-regardless of the terrain, enemy AT fire and the best efforts of enemy armour. Not really suited to the mobile war that unfolded... i think it's cool though.