Aside from another sparkling set of results at M&S, this week Stuart Rose announced a trial to charge shoppers 5p for its carrier bags - an initiative so devastatingly simple one wonders why rivals didn’t think of it before. They did, in the past, and both Lidl and Aldi still do, but the big four have been giving free bags for years. One reason: until recently, landfill wasn’t the national obsession it’s become. And Tesco argue charging for a plastic bag won’t actually change consumer behaviour; it prefers to reward bagless shoppers with Clubcard points. Or perhaps it’s the cost to the shopping basket. A few pence to a weekly shop can be the difference between winning and losing The Grocer 33. So, as of this week, we’re doing our bit with two new initiatives. First, to encourage other supermarkets to follow the M&S route, the cost of the shopping bags won’t be added to the totals in our 33; and second, when our mystery shoppers are asked to rate the service (which decides our store of the week), we’re adding a new criterion for checkout staff that ask if shoppers want to buy a bag for life.