Supermarkets appear to be disregarding Government pricing guidelines by using misleading discounts and special offers, according to an investigation.
Consumer group Which? analysed 459 "offers" to find multi-buy deals that cost shoppers more than buying the items separately just one week before, as well as "dubious" discounts and so-called special prices that were in place for most of the year.
Among the misleading deals was Iceland's offer of Kellogg's Crunchy Nut cereal at two packs for £4 when customers could have bought them individually for £1.49 a week earlier, the watchdog reported.
Asda labelled Wall's one litre Carte D'Or Strawberry Ice Cream as "was £3.50 now £2", despite selling the product at the lower price for more of the year than the higher price.
Morrisons promoted Cathedral City Mature Cheddar Cheese (350g) as "was £3.50 now £2" for the week of September 17 last year when the product had been available for the lower price of £2 the month before.
The Government rolled out new guidance to ensure that retailers complied with consumer law over pricing practices after Which? lodged a "super complaint" with the Competition and Markets Authority (CMA) into the issue in 2015.
The rules state that retailers must ensure the information they present to consumers is fair and does not waste time or cause annoyance, disappointment or regret.
In addition, information must not cause a consumer to overspend or buy a product that is inappropriate for them.
However, Which? said its latest investigation appeared to reveal that many UK supermarkets continued to flout the rules by offering deals that do not necessarily constitute a legitimate saving.
It urged shoppers to be vigilant of "dodgy deals", but is also demanding that supermarkets comply with Government guidelines and provide clearer pricing.
Which? said it would be reporting its findings to the CMA.
Natalie Hitchins, Which? head of home products and services, said: "Four years on from our super complaint on misleading pricing practices, many of the big supermarkets are clearly still in the wrong, with numerous examples of dodgy discounts and never-ending offers.
"These retailers must stop tricking shoppers with deceptive deals and spurious special offers. If not, the CMA must intervene to ensure that pricing guidelines are followed."
An Iceland spokeswoman said: "We update our promotions throughout the year to offer the best possible value to our customers, and review our approach to pricing structures to ensure savings to the customer are as transparent as possible.
"We have incorporated the findings shared by Which? into this process and will continue to review and improve our promotional calendar."
Tom Ironside, director of business and regulation at the British Retail Consortium, said: "Supermarkets seek to provide the best value for consumers on the hundreds of thousands of product lines they sell. This is often through promotions and discounts, which can change week to week, even on the same product lines, as retailers seek to cut the cost for shoppers."