Eight supermarket chains in Britain have agreed to ensure that special offers and price promotions are fair.
The Office of Fair Trading has been investigating the way prices are displayed, advertised and promoted in stores.
It raised concerns about prices being artificially inflated to make later discounts look more attractive.
The BBC reports that eight supermarkets have now agreed to adopt a set of principles drawn up by OFT. They are: Tesco, Sainsbury's, Morrisons, Waitrose, Marks & Spencer, Aldi, the Co-op and Lidl.
Asda has not yet signed, but said it was considering the revised code.
"Shoppers should be able to trust that special offers and promotions really are bargains," OFT chief executive Clive Maxwell told the BBC.
"Prices and promotions need to be fair and meaningful so shoppers can make the right decisions. Nowhere is this more important than during regular shopping for groceries.''
Items that suggest they are "better value" because they are in a "bigger pack" must have a comparable product elsewhere in the same store,
"Half price" or "was £3, now £2" offers must be sold at the new discounted price for the same, or less, time than the previously higher price.