You could be paying four times as much for the same branded groceries depending on which supermarket you use, according to a new investigation.

Which? has found Asda to be the cheapest supermarket in a survey of 493 items across six major supermarkets.

The investigation found Waitrose and Ocado were the most expensive.

Budget supermarket chains Aldi and Lidl were not involved in the research due to the fact they stock fewer branded goods.

Across all the 19 categories, 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.

Muller Light Greek Luscious Lemon yogurts fluctuated substantially in price at Sainsbury’s between £1 and £2.75 – a 175% 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, Which? found.

Other price variations included Carte D’Or Vanilla Ice Cream and Loyd Grossman Tomato and Basil Sauce at Asda, of 133% and 125% respectively.

Jordans Country Crisp Four Nut Cereal at Tesco cost £1.35 on some days and £3 on others, a variation of 122%.

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.

Almost all the products in the investigation varied in price and could be found discounted at one or more supermarkets at any time. However, a Which? survey found one in five shoppers are confused by grocery promotions and the majority (73%) would prefer consistently low prices.

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.”

An Ocado spokeswoman said: “Ocado is committed to offering customers the best range, service and value in the market. As part of this commitment, we are proud to offer over 49,000 products – more than any other supermarket.

“The fluctuation in price for the Lavazza product was due to a technical error and has since been resolved. The regular price is now back in place and is in line with most other major grocery retailers.”

Waitrose said: “We constantly review prices to ensure that we offer the highest quality products at fair prices, combined with fantastic customer service.”