I've just picked this thread up... gosh, memories...
The worst car for icing was the Hillman Imp, both carburettor and driver! It was essential to jeep varying the revs by changing gear. With the endine at the back and the so called heater at the front it was impossible to get the car warm. A car rug for the passengers legs, gloves and a hat too.
The Ford Prefect didn't have a heater at all, the tyres were virtually free of any grip in the cold, I used to be able to do a low speed 360 on any iron manhole cover...
Today we are spoilt, even in a Morgan....