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LONDON - FEBRUARY 29: Shoppers leave a Sainsburys store with their purchases in plastic bags on February 29, 2008 in London, England. The Prime Minister Gordon Brown has stated that he will force retailers to help reduce the use of plastic bags if they do not do so voluntarily. (Photo by Cate Gillon/Getty Images)

LONDON - FEBRUARY 29:  Shoppers leave a Sainsburys store with their purchases in plastic bags on February 29, 2008 in London, England. The Prime Minister Gordon Brown has stated that he will force retailers to help reduce the use of plastic bags if they do not do so voluntarily.  (Photo by Cate Gillon/Getty Images)