Crikey Clive, you don't hang about do you!
I really, really tried not to add to this debate as we're just covering old ground... again.
The term 4x4 that we are all using refers to the "off road" vehicles that are oversized, over heavy and downright dangerous. Not 4 wheel driven road cars.
The Scoda etc would be taxed as a normal car, as I think (hope) you already know.
The 4x4 cars are dangerous (and this is the important bit) to "other" road users as they are too heavy, to high and have little crumple zone. This means that, during a crash with a normal car, the 4x4 car passengers have more chance of survival "at the cost to the normal road user". They are desinged for impact with little damage to itself and this makes them a hazard on roads.
I travel a lot through small country roads, many with only one lane and most, if not all, the 4x4 drivers coming the other way keep their road postion and speed and use the cars weight and size to bully the other road users.
I think I've answered all your points, but I'm sure you'll let me know if I've missed anything.