From tomorrow, The Single Use Carrier Bags Charge (Scotland) Regulations 2014 will automatically assume that everyone in Scotland who requires a new carrier bag to take goods away is either intending to commit a littering offence or contribute it to landfill immediately.
The law isn't simply concerned with waste plastic as it covers paper bags too, and explicitly "multiple use" bags require more plastic. The intent appears to be to reduce the number and change the type of bags in circulation. A total ban would be more effective.
It's unlikely to help reduce littering, that would defeat the point of having a bag to carry goods away. The majority of visible litter appears to be in the form of used food and drink containers. People who litter don't care about the effect it has, don't consider their actions to be wrong, and won't be impacted financially by an extra 5p charge per bag. A ban on smoking would eliminate a lot more litter than the tiny percentage caused by carrier bags.
Only "single use" bags are affected under the regulations. Any bag labelled for "multiple reuse" and infinitely replaced by the manufacturer when worn out does not attract a charge, even if the purchaser throws the bag out the car window when they leave the store. Bags as thick as 50 micrometers or more also do not attract a charge, so don't forget your digital callipers when shopping.
The current "single use" bags can already be reused dozens of times. For the consumer a 5p charge still makes them the best value option. To encourage use of more efficient bags, the "multiple use" bags would have to be free.
Nothing in the regulations requires charging for "multiple use" bags, and these bags must be replaced free of charge forever. Driven by the need to maintain a supply of replacement free bags supermarkets may eventually stop providing "single use" bags (which they will make no profit from) and only provide "multiple reuse" bags that are priced to cover all the replacements.
Thicker bags have to be used 4-5 times as much as the thinner bags they replace to offset the extra environmental impact.