That’s about ads, not sticker price on the shelf, and about a lack of obligation to sell at that price. It does not say that it’s alright to lie and charge a different price at the register.
> A display of goods for sale in a shop window or within a shop is an invitation to treat, as in the Boots case, a leading case concerning supermarkets. The shop owner is thus not obliged to sell the goods, even if signage such as "special offer" accompanies the display. […] If a shop mistakenly displays an item for sale at a very low price it is not obliged to sell it for that amount.
From the Wikipedia article:
> A display of goods for sale in a shop window or within a shop is an invitation to treat, as in the Boots case, a leading case concerning supermarkets. The shop owner is thus not obliged to sell the goods, even if signage such as "special offer" accompanies the display. […] If a shop mistakenly displays an item for sale at a very low price it is not obliged to sell it for that amount.