When I first moved up here I thought the same, Sylvia and Russ - don't mind getting wet, walking or working will keep you warm until you get indoors, and then if it's warm enough let the clothes dry on you, or otherwise take them off, dry off and put on dry clothes. Sorted.
Then I moved up here. BH looked at me quizzically when I said the above. I soon learned - when it's wet here it's usually, and in winter and late autumn always, cold and wet. Mind- and finger-numbing cold wet that no amount of body heat generated through work will overcome. My reaction to the plastic mac / bin liner idea was initially the same as jaykay's - we're both in Cumbria, the idea of going outdoors in nothing but a plastic mac in winter is insane. Then I remembered that Sylvia and Russ are both down south, and I remembered routinely going down to let my chickens out wearing only a waterproof coat and wellies... I do miss the warmth of the Exmoor climate, I have to say. But boy, do I know a lot more now about how to keep oneself warm!