It's my understanding that although the bags do break down the little bits of plastic that are left NEVER will and those are the bits that will clog everything up. Here in Wales we have to buy the plastic bags if we need them instead of the shops/supermarkets just handing them out by the millions, but mostly we all use fabric bags or buy the Bags for Life as sold by the supermarkets. I for one am just too mean to pay 5p for a plastic bag! It has made a huge difference to the problem of plastic bags just being discarded and now we almost all carry our own bags where ever we go.