On further reflection tesco are definitely at fault.
The reason is that tesco are displaying two prices for a single product, and charging the higher price at the till.
If someone wants to buy one truffle at 2.24, and instead buys two.. they have been defrauded if they are charged 6 euros, and not 4.48. (even if a sign is displayed showing that €6 price, as there's another sign showing 2.24 each)
The reason they have been defrauded is because Tesco do not ask at the till if you want to buy two singles (at 2.24 each),.. or 'a special offer', at 3 euros each. Since Tesco do not ask what way you intend to purchase, and instead simply hoist the higher price on you,.. for that reason it is a deliberate attempt to defraud by tesco.
Their defence will be 'it was a mistake'.. which doesn't exonerate them in my opinion,.. they make too many 'mistakes'