Give or take a bit I would consider asda and tesco to be just about in the same price range.
However, I sometimes get the feeling that the asda smart price range covers a wider variety of products so it might be asda that works out slightly cheaper. I dunno though, perhaps it depends on the size of the store because you can ger massive asdas with a bigger range and small asdas where this is not so much the case.
If you shop at the time of day when stuff is reduced, even marks and spencers can be in budget. I go there when I can for cheap sandwiches and meat and fish sometimes.