Shoppers could be paying almost four times as much for branded goods depending on the day they shop and the supermarket they choose.

Consumer champion Which? has conducted what it says is its 'biggest ever supermarket pricing investigation', analysing a million prices for 493 grocery items at six major supermarkets.

Products at Asda, Morrisons, Ocado, Sainsbury’s, Tesco and Waitrose were all involved in the pricing structures study, which also revealed the cheapest retailer for branded items.

Lidl and Aldi were not included because they don't stock a comparable level of branded items.

The investigation, says Which?, showed shoppers could be paying well over the odds for the same product depending on the days they shop. The study also revealed which food and drink items are most prone to big price changes.

Lavazza Qualita Rossa Ground Coffee (250g) at Ocado had one of the most dramatic price differences - jumping from £1.30 for 63 days in 2020 to £5 for 130 days. Ocado, said the 284% price fluctuation was a technical error that has now been corrected and the price moved in line with other retailers.

The price for Müller yogurts was also hiked and slashed with Light Greek Luscious Lemon yogurts at Sainsbury’s flipping between £1 and £2.75 at roughly three week intervals – a 175% difference. The same product was also available for £1 or less in at least one of the other major supermarkets for about 85 per cent of the year, said the research.

Other products to have significant price variations included Carte D’Or Vanilla Ice Cream and Loyd Grossman Tomato and Basil Sauce.

At Morrisons, shoppers could pick up a bottle of Shloer’s Red Grape Juice Drink for just £1 on a good day, however it would cost more than double (£2.25) on others while Jordans Country Crisp Four Nut Cereal at Tesco also jumped by more than 120% ranging from £1.35 at its cheapest to more than double the price at £3 on other days.

Prices for branded cakes and biscuits also fluctuated by 48% with a 10-pack of Cadbury Chocolate Mini Rolls from Asda having one of the biggest price differences costing £1.20 at its cheapest up to £2.60.

Shoppers should also keep a close eye on the price of juices and smoothies, as prices in this category varied by 41%, followed by cooking sauces at 38% and cereal at 35%.

But across all 19 categories of food and drink analysed, Asda had the lowest average prices for branded groceries, says Which?, 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.

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.”

Supermarkets and shops will also begin charging double for carrier bags from today (Friday, May 21). Read more about the change here.

For more news on big brands and good places to enjoy a tasty bite, head to our Eat, Drink, Shop section