I will pay for carrier bags when:
Supermarkets stop wrapping cucumbers, peppers, mushrooms, swede, cauliflower, lettuce, apples, oranges, pears and all other fruit and veg in plastic shrink wrap, plastic bags and/or moulded plastic boxes. I bought a pack of 4 large open cup mushrooms the other day. They were carefully packaged in a specially designed plastic container, with a circle for each mushroom and then the whole thing was shrink wrapped.
Bin bags are free. My kitchen bin is designed to use carrier bags. Pointless using a bag for life and buying kitchen bin bags.
Fresh meat isn't sold on a polystyrene tray with a strange plastic thing between the tray and the meat and the whole thing shrink wrapped in plastic.
Frozen food such as salmon fillets isn't sold in a big polythene bag with each fillet shrink wrapped in its own plastic bag;
The plastic in my pack of jaffa cakes doesn't weigh more than the jaffa cakes.
They stop selling individual portions of salad in a plastic tub with its own plastic knife and fork.
They stop selling bin bags wrapped in plastic.
They stop selling magazines shrink wrapped in plastic.
They stop selling fresh cream cakes in plastic boxes.
The list is never ending. Carrier bags are the least of the problem.