you dont really get best AND cheapest..
But Lidl is pretty **** quality, and doesn't have many brands (apart from foreign ones)
Asda is a good, cheap supermarket which stocks all the brands including their own, so you can go and spend a lot or a little.. and you can choose which things to scrimp on and which to save on all in one shop.
they also have home stuff, clothes (great!), entertainment, a bakery, fishmonger, pizzeria, deli counter, butcher, photo developing, hairdresser and chemist.. great shop.
there is one at the Jewel and one at the Corn Exchange.