A) 50p for an "ordinary" plastic bag
B) £1 for one of those indestuctible heavy weight plastic-hemp like bags
C) 10p for (its not quite common/invented yet) biodegrable in a reasonable amount of time bag (which you can use again and again, obviously) Bag for life thingy that they already do, but a really eco friendly one
D) free - bio-deg, yoghurt woven, etc . . (but not very good for more than a few items)

I'd probably remember when shopping to take all of the "B" bags I'd bought, if that were the case,and I know (hope!) Merrick will have a better answer to this, but its ruminating in me..
i remeber they used to charge 2p a bag 20yrs ago, but it "went out of fashion" as it were .. .

Im probably wrong, cos it seems quite obvious, but a LOT of people would re-use their 10p biodegradable bags, but a LOT would buy the expensive ones - which would offset the cost of the bio-deg ones. . etc etc etc

oh, and "polluter pays" MUST be a good idea ...

rant over
t xxxx