Say 'Bogof' to supermarkets' dodgy deals Mr Maxwell said that the principles taken together with previous guidance provide supermarkets with a clear benchmark for how they should be operating so that their food and drink promotions reflect the spirit as well as the letter of the law. However, the agreed code is not legally binding and the supermarkets will not be held accountable for the changes. The OFT has admitted that the principles "do not come into force on any particular date so whether customers see any changes will remain to be seen." Richard Lloyd, executive director at consumer group Which?, said that the OFT has now made clear to supermarkets what is off limits when they promote products with special offers or discounts, but this did not go far enough. "When household budgets are squeezed and food prices are one of people's top financial worries, it's unacceptable that shoppers are confused into thinking that they're getting a good deal when that might not be the case," he said. Regulators should be prepared to take enforcement action against traders found breaking the rules. Misleading advertising is illegal under the 2008 unfair trading regulations. The regulator said it did not discover any illegality during its investigation, but did find some "inconsistency" in the way the law was interpreted and applied. An earlier investigation by Which? suggested that some supermarkets had mislead customers over discounts and multi-buy offers. It analysed more than 700,000 prices and suggested that in some cases the "discounts" ran for much longer than the original price. Some supermarkets later admitted isolated errors amid a huge volume of pricing. When you are pushing your trolley around the supermarket, be aware that these perfectly honed marketing environments are benefiting from millions of pounds of research into how to encourage and seduce you into buying and spending more than you need. So with about four in 10 of all products sold in supermarkets on some kind of special offer, consumers must take matters into their own hands to ensure they are not being duped. Here is how to watch out for three sneaky tricks. Compare carefully Watch out for comparison tricks. Some supermarkets will charge different prices on items in a number of branches and then advertise the discount despite the fact that the more expensive item was never sold in that shop. Another ploy is advertising that items offer better value because they are in a bigger pack. Similarly, saying a product price has been reduced without mentioning that this is because the package size has shrunk can also mislead shoppers. To ensure you are not paying more than necessary check the unit price on the sticker. In most supermarkets, food will be clearly priced by weight or volume across all stores to make it easier for consumers to compare products and spot the best deals. Beware yo-yo pricing Many retailers sell products at an inflated price for a limited period in a few branches, then roll them out across all stores at a lower price - known as "yo-yo pricing." The "discount" price period lasts much longer than the original higher price period, making the discount price really the normal selling price. Bigger is not always better Buying in bulk is not always more economical. For instance, with buy-one-get-one-free deals, shoppers can pay more than if they bought the same in a larger pack. Which? looked at the price of 115 different products at Waitrose, Tesco, Asda, Sainsbury's and Ocado and found that around 10pc increased in price when offered as part of a multibuy.