The Advertising Standards Authority decided the supermarket breached rule 3.1 (misleading advertising) of the code of practice.
Tesco advertised four 44cl cans of Hobgoblin for £4.50 on October 23, calling it a 49p saving on the original price of £4.99, and a yellow sticker said the deal would run until November 12.
A customer complained that the beer had been available for £4 for three months until October 7, and was still being sold at the lower £4.50 price after the promotion ended.
Tesco said the beer had been priced at £4.99 from October 2 until October 22, and said it continued to sell it at £4.50 after November 12 to compete with rivals.
But the ASA said: “Although we acknowledged that the product category was one in which prices fluctuated regularly, we considered that, because the product had been available at £4 for at least two of the three months leading up to the promotion, and for at least twice as long as it had been available at the higher price referenced in the ad, it was reasonable to assume that £4 was the normal selling price for the product at the time the ad was seen.
“Because of that, and because we considered that the ad implied that £4.99 was the normal selling price for the product, we concluded that the promotion was likely to mislead consumers into believing that a greater saving was available than was the case.”
It added: “We noted that the ad stated ‘was £4.99, now £4.50 valid from 23/10/2013 until 12/11/2013’ and considered that consumers were likely to understand that, in order to take advantage of the 49p price reduction, they would need to take the offer up by the advertised end date of November 12 and the price would therefore revert to £4.99 after that date.
“However, we understood that the price remained £4.50 until December 3. Although we acknowledged that this reflected a price reduction and was not a result of the promotional end-date being extended, we considered that the inclusion of a closing date in the ad implied that the price would be increased to £4.99 after that date.
“Because that was not the case, we concluded that the ad was likely to mislead in that respect.
“The ad must not appear again in its current form. We told Tesco to ensure that prices used as the basis of savings claims reflected the normal selling price for the product and not to imply that a product would revert to a higher price if that was not the case.”