Supermarket prices go up and down dramatically day by day, an investigation has revealed.
Analysis of 493 items by consumer watchdog Which? found cake and biscuits fluctuated most.
Coffee, ice cream, yoghurt and soft drinks all bounced up and down too.
Which? checked prices at Asda, Morrisons, Sainsbury’s, Tesco, Waitrose and Ocado throughout 2020.
It found Muller Light Greek Luscious Lemon yogurts flipped from £1 to £2.75 at Sainsbury’s at three-week intervals.
At Morrisons Shloer’s Red Grape Juice Drink was £1 some days, £2.25 others.
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At Ocado, Which? found Lavazza Qualita Rossa Ground Coffee (250g) was £1.30 on 63 days but £5 for more than a third of 2020.
Which? said the so-called “high-low” tactics used by supermarkets mean shoppers could be paying over the odds.
The research found significant price differences for Carte D’Or Vanilla Ice Cream and Loyd Grossman Tomato and Basil Sauce at Asda, with prices fluctuating by 133% and 125% respectively.
And at Tesco the cost of Jordans Country Crisp Four Nut Cereal varied from £1.35 on some days to £3 on others, leaving some shoppers paying 122% more for a packet if they picked the wrong day to do their shopping.
Which? said savvy shoppers should keep a close eye on the price of juices and smoothies as prices varied by 41% on average.
The cost of cooking sauces varied by 38%, crisps 36% and cereal 35%.
Asda had the best prices across all 19 categories. A spokesman said it was “pleased” at the finding.
Ele Clark, of Which?, said: “People are at risk of massively overpaying for branded groceries depending on when and where they shop.”
Ocado said the fluctuating Lavazza price was down to a “technical error” that has now been fixed.
Sainsbury’s said: “Prices fluctuate up and down for a variety of reasons.”
A Tesco spokesperson said: “At Tesco, we know our customers want competitive prices for the products and brands they buy regularly. That’s why we’ve simplified our range, reduced the number of promotions and held prices low so that customers can get simple, stable prices.
"We’re also matching Aldi on hundreds of branded and own-brand items through our Aldi Price Match and offering great savings through our Clubcard prices.”
