Small stores, mostly own labels and fewer employees. They buy only packages that don't need unpacking, saving a lot of time getting products on the shelf. Employees work all positions in the store so that shelves are filled when it's less busy and everyone is at the checkout when needed. That way no employee is idle, saving salaries.

In the UK they also profit from their European footprint. If you go somewhere else in Europe, you'll find that most products (nearly everything except for some food items) are the same as in the UK. They can buy in much bigger amounts than even Sainsbury's or Tesco as they operate in most European countries.