The prices are the same, but the selection is different. The small stores typically don't stock any budget brand goods, they only stock the average and luxury version.

They've out-competed a huge number of independent stores, since the supply chain of Tesco allows them to keep the small store well-stocked at relatively small cost, and with less floor space needed for a stock room. A lorry drops off two or three pallets of goods at the small store on its way to a supermarket. An independent shop can't compete with close to free delivery and the purchasing power of Tesco.

I used to live 5 minutes walk from a Tesco Express, and did almost all my food shopping there. I'd only go to the supermarket (15 minutes cycle away) if I'd run out of something unusual.

The prices aren't much different to the full-size stores, but they (understandably) only stock the small sizes of everything. You wouldn't buy in bulk there.