Ah, but don't forget that whilst the C does indeed have more fuel and goes further than the other variants - we couldn't possibly buy it because we tried to buy it once so a re-attack would make us look stupid and we would have to admit that wheel equipped naval jets were able to operate from surfaces other than boats. And in any case the A model is the Air Force variant so we need to buy that because we're an Air Force. Also it doesn't have a probe so we could spend more money fitting one, or fitting a boom to Voyager - whichever works out more expensive.
An attribute of the C that we didn't mention last time we touched on this subject Orca is that it can carry significantly more ordnance than the A or B on its underwing hardpoints, which would likely be the configuration that the UK would fly most often.
All things considered, I do now think a mixed fleet of Bs and Cs is probably the best suited to our requirements (the lack of a probe being the A's biggest handicap), but as has been said I don't see how the government could perform the double U-turn necessary to get it.