I imagine the difference in prices between the big supermarkets very much depends on what you buy. For some, ASDA may be cheaper, for others Morrison's. We use ASDA (and M&S) mainly but that's because there is a big one near to where we live, which is also the nearest supermarket of viable size to permit us to do our weekly shop. I am sure if Tesco was closer, we'd probably use that. We do vary it a bit though and find all stores are much of a muchness regarding price, provided they are of a similar size.