IIRC during WWII when the Allies invaded Sicily, the British left behind all their indigenous tanks with the exception of the Churchill. (Which does reinforce the point about heavy armour.) Also the majority of the tanks the British took to Normandy were American Shermans.
Given that we have our own 'not invented here' syndrome I do agree that it is far more probable that the V.1 canon Challenger 2 would be the tank of choice.
Thanks for all the input.
