According to Which?, shoppers could be paying almost four times more than they need to for the same branded grocery products at certain times.

The consumer champion’s supermarket pricing investigation analysed more than a million prices for 493 branded grocery items at Asda, Morrisons, Ocado, Sainsbury’s, Tesco and Waitrose throughout 2020.

The investigation found that shoppers could be paying over the odds for the same products depending on the days they shop. It also identified the types of grocery products that fluctuate the most when it comes to price.

Products with the most fluctuating prices

Lavazza Qualita Rossa Ground Coffee (250g) at Ocado had the most dramatic price difference, as the investigation found shoppers could pay almost four times more for the same product on different days.

It was at its cheapest price of £1.30 for 63 days in 2020, however for more than a third of the year (130 days), it cost £5 – a 284% difference for the same product. Ocado said this price fluctuation was an error that has now been corrected.

The price for Müller yogurts illustrated the so-called ‘high-low’ tactic used by many supermarkets – when prices are dramatically hiked and then slashed at regular intervals. For example, Müller Light Greek Luscious Lemon yogurts fluctuated substantially at Sainsbury’s during 2020, flipping between £1 and £2.75 – a 175% price difference – at roughly three-week intervals. The same product was also available for £1 or less in at least one of the major supermarkets for about 85% of the year.

Other products that saw significant price variations included Carte D’Or Vanilla Ice Cream and Lloyd Grossman Tomato and Basil Sauce at Asda – with prices fluctuating by 133% and 125% respectively.

At Morrisons, shoppers could pick up a bottle of Shloer’s Red Grape Juice Drink for just £1 on a good day, however it cost more than double (£2.25) on other days, a 125% increase.

The investigation also analysed pricing at a category level, looking at 19 areas from chocolates to cheese, and found the price for branded cakes and biscuits fluctuated by 48% on average – more than any other category.

In this category, Which? analysed the price of 14 products and found a 10-pack of Cadbury Chocolate Mini Rolls at Asda had the biggest price difference. It cost just £1.20 at its cheapest but was more than double the price at £2.60 on certain days.

Which is the cheapest supermarket?

Across all 19 categories analysed, Asda had the lowest average prices for branded groceries, making it the best option for shoppers who prefer branded items but do not want to pay over the odds.

Waitrose was the most expensive supermarket for branded items in eight categories including energy drinks, ice cream and tea, and Ocado for seven categories including juice drinks, coffee and cheddar.

While Aldi and Lidl were not featured in the investigation, as they stock fewer branded goods, both budget supermarkets have won legions of customers by focusing on consistently low prices rather than deals and discounts. In Which?’s monthly price analysis, the cheapest supermarket is invariably either Aldi or Lidl.

Ele Clark, Which? Retail editor, said: “Our research reveals just how wildly food and drink prices can fluctuate from day to day, meaning people are at risk of massively overpaying for branded groceries depending on when and where they shop.

“We would recommend keeping an eye on the prices of your favourite products and stocking up when they’re discounted to avoid paying over the odds.”