Earlier quoted context omitted.
Well apparently a 5p charge resulted in a 14x decrease in usage of plastic bags, so despite your anecdote, it does make a difference.
Fair enough but I wonder how much of that has to do with simply being asked? Being given a bag was standard, as normal as expecting the store to be heated. An invisible service. Now, you don't get given a bag for your Sandwich & Water at lunch, and you don't get a free bag with your McDonalds meal to name just a couple of services. 1p or 5p wouldn't make much of a difference? A Family paying 100 pound a week on shopp…
https://market.subwiki.org/wiki/Zero_price_effect
The same acts in reverse.
I personally reuse the same bag every time I go shopping until it is damaged. When I walk to my local, I carry the two or three items I bought directly, rather than in a bag. I could afford to buy over a million plastic bags a year, yet I've changed my behaviour to avoid buying them whenever possible.
(In my case, it has nothing to do with being asked, as I invariably use the automated checkout machines. Bags are available for purchase adjacent to these machines, so it's not an availability problem either.)