When Asda decided to flog 10 of its most popular products at 50p each last weekend, its marketing team was in such a rush to publish adverts that it forgot to read its own small print.

Buried at the bottom of the press adverts, which offered discounted best-sellers such as bread and butter for one weekend only, it read that the 50p offer was valid until 29 July. It should have read 29 June.

"As far as the misprint is concerned, we won't be honouring it," said an Asda spokesman.

Peter McCarthy, from the Which? legal team, said Asda had no obligation to honour the stated date. "The consumer would not be able to force Asda to sell at 50p," he said. "It is exactly the same as when an item has the wrong price on it in a shop, the shop has no obligation to sell it for that price."

However, Julian Connerty of Clyde & Co law firm said Asda may be bound to the advert. "It is an offer to sell and if accepted they are bound to it," he said.