But, according to a survey from environmental risk consultancy Trucost, the real retail eco-hero is not one of these big names - who for all their bluster are relative newcomers to the game - but rather the dear old Co-op.
Manchester's finest has been in the green game since way before it got fashionable, pioneering a switch to green electricity back in 1998 - now 98% of the juice it consumes is environmentally friendly. What's more it's covered its famous Mancunian HQ, the CIS Tower in solar panels and has even built its own wind farm in Cambridge. How's that for commitment?
In second place comes M&S, whose efforts over the last year or so have paid off, then Tesco in third, another latecomer to greenery which has moved fast in recent months. Sainsbury's can only manage sixth place, perhaps because its published environmental data is less recent than for some of the others. Bringing up the rear in 10th place is Somerfield, with Morrisons in ninth. Oh dear.
The survey looks at the companies carbon emissions and the percentage of waste they produce that is not recycled. The results are expressed as a cost per million pounds of sales - Co-op scoring a thrifty £324/£m sales, Somerfield a whopping £1,195/£m. ‘We want to answer a very specific question - for the economic benefit they generate, what is the environmental impact of these companies?' says Trucost's Simon Thomas.
However, such direct emissions are only part of the bigger environmental impact of our mega-retailers, says Thomas. ‘In many ways the real story is not in direct emissions, but rather in the carbon emission embedded in the goods they sell. We estimate that these could be up to 30 times as much as direct emissions. The most important thing that supermarkets can do to address these embedded emissions is to start buying better from an environmental perspective' he says. Here at MT we think that's a sound idea - if there's one thing our top retailers know how to do, it's buy well.
The full results of the survey will be revealed in tonight's Money Programme, on BBC 2 at 9.30pm.