Which claims retailers are “confusing consumers with tactics that exaggerate discounts and manipulate shoppers”, arguing they create “the illusion of savings that don't exist”.
The complaint comes on the back of news last week that brands were reducing the size of their products while supermarkets were continuing to charge the same or more for the item.
In 2013, the UK spent around £115bn on groceries, of which it is estimated 40 per cent was sold on promotion. Which claims consumers are collectively losing out on hundreds of millions of pounds because of these tactics.
Which has identified three key areas of concern – multi-buys, the idea that a larger pack is better value and seasonal offers.
What Which says about multi-buys
Asda increased the price of a Chicago Town Four Cheese Pizza Two-Pack from £1.50 to £2 as it went onto multi-buy at two for £3. It went back to £1.50 as the ‘offer’ ended (2014).
What Which says about “larger pack, better value”
Tesco sold four cans of Green Giant Original Sweetcorn for £2 (was £2.44), but six cans were proportionately more expensive, at £3.56. That’s despite the fact the larger pack said ‘special value’ (2014).
What Which says about seasonal offers
We found a Nestle Kit Kat Chunky Collection Giant Egg was advertised at £7.49 for just 10 days in January at Ocado, but then sold on offer at £5 for 51 days (2015).
“These tactics manipulate consumer spending by misleading people into choosing products they may not have picked if they knew the full facts,” the group said.
Executive director, Richard Lloyd added: “'Despite Which repeatedly exposing misleading and confusing pricing tactics, and calling for voluntary change by the retailers, these dodgy offers remain on numerous supermarket shelves. Shoppers think they’re getting a bargain but in reality it’s impossible for any consumer to know if they’re genuinely getting a fair deal.
“We’re saying enough is enough and using one of the most powerful legal weapons in our armoury to act on behalf of consumers by launching a super-complaint to the regulator. We want an end to misleading pricing tactics and for all retailers to use fair pricing that people can trust.”
The CMA has 90 days to decide whether to proceed with an investigation. But not everyone believes this could yield any results for consumers.
Clive Black of Shore Cap said: "There will probably be a prolonged inquiry, which can be expected to draw upon a vast array of senior management time, no doubt embellished with lashings of legal counsel.
"In the meantime shoppers of the UK, which should be effectively protected by the authorities from law-makers to local trading standards officers it should be said, so what are they doing, move on, living in a real word and not a parody of a Whitehall farce where non-fiction becomes reality."