We have the same problem here where I work.
We have been told we are not to give bags unless the customer asks.
Almost every customer has a bag even the kids when they buy a few sweets, although I'm sure that's so they can go around the store and put a few more in their bag.
We are now only allocated a limited amount of bags.
Senior citizens are the least bother,the majority of them always bring their own reusable bag.
I think a charge will soon be brought in, which I can see will cause all kinds of upset amongst customers,however I do think it's a way around the problem.
I even have people coming in asking for a carrier bag, because their dog has done it's business on the street and they had forgotten to bring their own bag.
It's the worst of two evils really... do you leave the mess on the street for a passer by to walk in and maybe carry into the store.. or do you just give yet another carrier bag!!