This is such an important point! A relatively tiny charge had a massive impact on consumer behavior. This is real-world efficient market theory. If you put 5 cents on the counter and say "take it if you want it" then people will take it. What we have learned is that 90% of bags were essentially not needed, and so only the lightest touch was required.

Punitive measures ("we should charge $1-2 for a bag") are counter-productive because the harm to society actually exceeds the benefit to society. We are not trying to eliminate every plastic bag at any cost. This is not a plastic bag crusade. The goal cannot be absolutism, it must be based on efficient market economics where the new regulation actually benefits society.

I think you are missing the point of my comment above.

Many, if not most supermarkets in the UK no longer have single-use bags at all. The 5p charge has become irrelevant because there are no longer any such bags.

BUT now they have reusable plastic bags, that are much sturdier and thus made of more plastic, that they sell for 10p.

Most people do bring their own reusable bags with them but some don't, and as said sometimes you simply did not plan to shop and simply don't have a bag with you. In such cases people end up paying 10p for these reusable bags and probably throw them away.

Therefore, I think that single-use bags are still have a valid use: Sometimes you need a bag just for this one time and it would be best if such a bag could use the least material possible. They don't have to be plastic.

The more expensive price is intended at ensuring that people buy them only in emergency cases. Reusable bags should also be sold for more than 10p so that people care enough to actually keep them for a long time.

Note also that the article mentions statistics about single-use bags. Those 10p bags are not single-use so don't appear at all in the figures! A cynic would suspect supermarkets have found a loophole here...