afaik you used to have to have a card as they operated as a cash n carry type store like macro rather than as a shop. in accordance to this, they could sell only to members not the general public. cards had a nominal membership fee to represent this. now, prices seem to have gone up, and the card is being given free as a reward card which entiles holders to purchase special deals (like 2 for £10 things). if you dont have a card, you'd have to pay full price for both items. however, some stores seem to be implementing the old system still, while others have big signs saying you no longer need a card.
edited to add: stores used to be just like big warehouses, no mannaquin displays and such like, while now its just like any other shop inside