Martin Hickman, consumer affairs correspondent for the popular United Kingdom newspaper The Independent, revealed in a late February article that, "Unpublished Government research suggests the plastic carrier may not be an eco villain after all—but, whisper it, an unsung hero." (Carrier in the English spoken in England means bag, specifically a shopping bag.) Hickman writes that a draft of the research report was obtained by The Inedpendent on Sunday found that high-density polythene bags used by shops are in fact greener than the supposedly low-impact alternatives.
How much greener? HDPE sacks are almost 200 times less damaging to the climate than cotton bags, says the report, and they emit less than one third of the CO2 emitted by paper bags. The report suggests that a cotton bag would have to be used every work day for a year, and a paper bag would have to be used at least three times, to balance out the impact of one HDPE bag.
Hickman's Independent article says the UK Environment Agency, which commissioned the report, says it is still being peer reviewed. It was submitted to the peer review process more than a year ago, and while the agency has no publication date as yet, it says that it will be soon. There's much more detail in the full article, which is well worth reading.