I would guess around £50 a week for 2 of us. I try and buy economically, but I am fussy and like brands, so I buy when things are on offer and shove them in the freezer.
I do a BIG shop once a month which costs about £240, but that includes booze and cleaning stuff. But every couple of days I nip to the nearest store and buy milk, bread, salad and fruit. Plus, if you go around 4:30pm they reduce a lot of their meat and fresh pies - so again, I stock up.