I have been reading some of the suppliers' horror stories of dealing with the big four and it has made me vow (again) to cut down on what I buy from them.
I already do pretty well and only visit a large store about once every 2 months.
I get an organic veg box and a meat box delivered. Almost everything else comes from Lidl. This justifies (to me) the increased cost of the organic meat and veg and is the only supermarket I can walk to. Plus I find their food/toiletries and cleaning stuff to be very good quality for the price. But, I have no idea if they are on the Tesco or Waitrose end of the scale ethically.