The supermarket giant advertised four cans of Hobgoblin on its website for £4.50 on October 23, claiming this was a 49p saving on the original price of £4.99.
A bright yellow shelf sticker said the deal was available until November 12.
But one 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, a total of 21 days. They said the price was consistent with other retailers in the market and believed that customers accepted £4.99 as a genuine price for the product.
They said they had agreed to adhere to the Office of Fair Trading’s guidelines on food pricing and promotions at the end of 2012, meaning that they would not advertise a product as being on promotion for a period longer than that product had been available at a higher price.
Tesco agreed that it continued to sell the product at £4.50 from November 13 to December 3 “to reflect other retailers’ selling price”, but this was not communicated to customers as a promotion and the price was featured on a regular white shelf label during that time.
The Advertising Standards Authority (ASA) said consumers were likely to understand that £4.99 was the usual selling price for the product and Tesco had reduced the price for the promotional period, meaning they benefited from a saving of 49p.
A Tesco spokesman said: “We aim to offer prices and promotions that help our customers manage the cost of their shopping.
Which? executive director Richard Lloyd said: “Special offers should be special. We’ve found dodgy deals across the aisles, with prices yo-yoing between multi-buys and discounts so that it is almost impossible to know the actual price.
“We’re campaigning for simpler, clearer and fairer pricing rules and tougher enforcement action.”