All five firms pledged to give clearer pricing information

It follows a study by the Office of Fair Trading (OFT), which found against Asda, Sainsbury's, Waitrose, Tesco, and dedicated online site Ocado

The OFT said all had failed to make clear that prices shown online could change before deliveries were made.

All five firms have now pledged to give better price information.

Customers have a right to clear and transparent information upfront when making their buying decisions OFT chief executive John Fingleton

The OFT launched its probe after customers complained that prices charged on delivery could be higher than those shown when they ordered online.

The discrepancy can arise because when goods are delivered people are typically charged that day's in-store prices. These can be higher than the prices that were displayed on the day the person made their order.

Better information

"Customers have a right to clear and transparent information upfront when making their buying decisions," said OFT chief executive John Fingleton.

The five retailers have agreed to give better general price information, and to ensure that the time limits to any special price offers are clearly shown on their websites.

Online grocery shoppers are also free to reject an order upon delivery if the price has changed from when they placed the order.

Waitrose's parent company John Lewis owns a minority stake in Ocado.