The trouble is that all that plastic really does make a difference when it's a supermarket chain as big as Sainsbury's. I remember reading about Tesco making their cheese plastic less floppy and how much that made a difference!
Our local council also doesn't recycle any plastic that isn't bottle shaped so, for us, that would be less plastic in our black bin which is a huge win when it is only emptied every fortnight. Would stretchy lids not go over the humous?