Yeah, it is pretty rich of Sainsburys and Anya Hindmarch. A blatant PR stunt (a pretty good one at that). If they really wished to contribute to saving the environment, then they'd have manufactured as many eco-friendly 'I am not a plastic bag' bag's as possible to ensure that as many people as people were using them. Shameless promotion.
And lets be honest, how many of the people that purchased them after queueing in the wee hours of the morning are going to use them to carry around onions and milk?